diff --git a/src/modules/admin/controllers/change-log.controller.ts b/src/modules/admin/controllers/change-log.controller.ts
new file mode 100644
index 0000000..2f2aa50
--- /dev/null
+++ b/src/modules/admin/controllers/change-log.controller.ts
@@ -0,0 +1,181 @@
+/**
+ * ChangeLogController - Controlador de Historial de Cambios
+ *
+ * Endpoints para consultar el registro de cambios de auditoria.
+ *
+ * @module Admin
+ * @gap GAP-007
+ */
+
+import { Router, Request, Response, NextFunction } from 'express';
+import { DataSource } from 'typeorm';
+import { ChangeLogService } from '../services';
+
+export function createChangeLogController(dataSource: DataSource): Router {
+  const router = Router();
+  const service = new ChangeLogService(dataSource);
+
+  // ==================== QUERIES ====================
+
+  /**
+   * GET /
+   * Lista cambios con filtros y paginacion
+   */
+  router.get('/', async (req: Request, res: Response, _next: NextFunction): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+
+      const filters = {
+        tableSchema: req.query.tableSchema as string,
+        tableName: req.query.tableName as string,
+        recordId: req.query.recordId as string,
+        userId: req.query.userId as string,
+        operation: req.query.operation as any,
+        fromDate: req.query.fromDate ? new Date(req.query.fromDate as string) : undefined,
+        toDate: req.query.toDate ? new Date(req.query.toDate as string) : undefined,
+      };
+
+      const pagination = {
+        page: parseInt(req.query.page as string) || 1,
+        limit: parseInt(req.query.limit as string) || 50,
+      };
+
+      const result = await service.findAll(tenantId, filters, pagination);
+      res.json(result);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /statistics
+   * Estadisticas de cambios
+   */
+  router.get('/statistics', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const fromDate = req.query.fromDate ? new Date(req.query.fromDate as string) : undefined;
+      const toDate = req.query.toDate ? new Date(req.query.toDate as string) : undefined;
+
+      const stats = await service.getStatistics(tenantId, fromDate, toDate);
+      res.json(stats);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /recent
+   * Cambios recientes
+   */
+  router.get('/recent', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const hours = parseInt(req.query.hours as string) || 24;
+      const limit = parseInt(req.query.limit as string) || 100;
+
+      const changes = await service.getRecentChanges(tenantId, hours, limit);
+      res.json(changes);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /by-user/:userId
+   * Cambios por usuario
+   */
+  router.get('/by-user/:userId', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const { userId } = req.params;
+
+      const pagination = {
+        page: parseInt(req.query.page as string) || 1,
+        limit: parseInt(req.query.limit as string) || 50,
+      };
+
+      const result = await service.getChangesByUser(tenantId, userId, pagination);
+      res.json(result);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /by-table/:schema/:table
+   * Cambios por tabla
+   */
+  router.get('/by-table/:schema/:table', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const { schema, table } = req.params;
+
+      const pagination = {
+        page: parseInt(req.query.page as string) || 1,
+        limit: parseInt(req.query.limit as string) || 50,
+      };
+
+      const result = await service.getChangesByTable(tenantId, schema, table, pagination);
+      res.json(result);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /history/:schema/:table/:recordId
+   * Historial completo de un registro
+   */
+  router.get('/history/:schema/:table/:recordId', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const { schema, table, recordId } = req.params;
+      const limit = parseInt(req.query.limit as string) || 100;
+
+      const history = await service.getRecordHistory(tenantId, schema, table, recordId, limit);
+      res.json(history);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /:id
+   * Obtiene cambio por ID
+   */
+  router.get('/:id', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const { id } = req.params;
+
+      const change = await service.findById(id);
+      if (!change) {
+        res.status(404).json({ error: 'Registro de cambio no encontrado' });
+        return;
+      }
+      res.json(change);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  // ==================== MANTENIMIENTO ====================
+
+  /**
+   * DELETE /purge
+   * Purgar registros antiguos (admin only)
+   */
+  router.delete('/purge', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const daysToKeep = parseInt(req.query.daysToKeep as string) || 90;
+
+      const deleted = await service.purgeOldRecords(tenantId, daysToKeep);
+      res.json({ deleted });
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  return router;
+}
diff --git a/src/modules/admin/controllers/index.ts b/src/modules/admin/controllers/index.ts
index bbd4d41..b0ea0f1 100644
--- a/src/modules/admin/controllers/index.ts
+++ b/src/modules/admin/controllers/index.ts
@@ -7,3 +7,6 @@ export { createCostCenterController } from './cost-center.controller';
 export { createAuditLogController } from './audit-log.controller';
 export { createSystemSettingController } from './system-setting.controller';
 export { createBackupController } from './backup.controller';
+
+// GAP-007: Audit Triggers
+export { createChangeLogController } from './change-log.controller';
diff --git a/src/modules/admin/entities/change-log.entity.ts b/src/modules/admin/entities/change-log.entity.ts
new file mode 100644
index 0000000..2899fbe
--- /dev/null
+++ b/src/modules/admin/entities/change-log.entity.ts
@@ -0,0 +1,83 @@
+/**
+ * ChangeLog Entity
+ *
+ * Registro automático de cambios a nivel de base de datos
+ * mediante triggers. Captura INSERT, UPDATE, DELETE en tablas críticas.
+ *
+ * @module Admin
+ * @table audit.change_log
+ * @gap GAP-007
+ */
+
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  Index,
+} from 'typeorm';
+
+export type OperationType = 'INSERT' | 'UPDATE' | 'DELETE' | 'TRUNCATE';
+
+@Entity({ schema: 'audit', name: 'change_log' })
+@Index(['tenantId'])
+@Index(['userId'])
+@Index(['tableSchema', 'tableName'])
+@Index(['recordId'])
+@Index(['executedAt'])
+@Index(['executedDate'])
+@Index(['operation'])
+export class ChangeLog {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  // Contexto
+  @Column({ name: 'tenant_id', type: 'uuid', nullable: true })
+  tenantId?: string;
+
+  @Column({ name: 'user_id', type: 'uuid', nullable: true })
+  userId?: string;
+
+  @Column({ name: 'session_id', length: 100, nullable: true })
+  sessionId?: string;
+
+  // Operación
+  @Column({ type: 'varchar', length: 10 })
+  operation!: OperationType;
+
+  @Column({ name: 'table_schema', length: 63 })
+  tableSchema!: string;
+
+  @Column({ name: 'table_name', length: 63 })
+  tableName!: string;
+
+  @Column({ name: 'record_id', type: 'uuid', nullable: true })
+  recordId?: string;
+
+  // Datos
+  @Column({ name: 'old_data', type: 'jsonb', nullable: true })
+  oldData?: Record<string, any>;
+
+  @Column({ name: 'new_data', type: 'jsonb', nullable: true })
+  newData?: Record<string, any>;
+
+  @Column({ name: 'changed_fields', type: 'text', array: true, nullable: true })
+  changedFields?: string[];
+
+  // Metadatos
+  @Column({ name: 'client_ip', type: 'inet', nullable: true })
+  clientIp?: string;
+
+  @Column({ name: 'user_agent', type: 'text', nullable: true })
+  userAgent?: string;
+
+  @Column({ name: 'application_name', length: 100, nullable: true })
+  applicationName?: string;
+
+  // Timestamp
+  @Column({ name: 'executed_at', type: 'timestamptz', default: () => 'NOW()' })
+  executedAt!: Date;
+
+  // Campo generado (solo lectura)
+  @Column({ name: 'executed_date', type: 'date', insert: false, update: false })
+  executedDate?: Date;
+}
diff --git a/src/modules/admin/entities/index.ts b/src/modules/admin/entities/index.ts
index 9276d74..125801e 100644
--- a/src/modules/admin/entities/index.ts
+++ b/src/modules/admin/entities/index.ts
@@ -8,3 +8,6 @@ export * from './audit-log.entity';
 export * from './system-setting.entity';
 export * from './backup.entity';
 export * from './custom-permission.entity';
+
+// GAP-007: Audit Triggers
+export * from './change-log.entity';
diff --git a/src/modules/admin/services/change-log.service.ts b/src/modules/admin/services/change-log.service.ts
new file mode 100644
index 0000000..09a8101
--- /dev/null
+++ b/src/modules/admin/services/change-log.service.ts
@@ -0,0 +1,254 @@
+/**
+ * Change Log Service
+ * ERP Construccion - Modulo Admin
+ *
+ * Consultas sobre el registro de cambios de auditoria (triggers).
+ * @gap GAP-007
+ */
+
+import { Repository, DataSource, Between } from 'typeorm';
+import { ChangeLog, OperationType } from '../entities/change-log.entity';
+
+// DTOs
+export interface ChangeLogFilters {
+  tableSchema?: string;
+  tableName?: string;
+  recordId?: string;
+  userId?: string;
+  operation?: OperationType;
+  fromDate?: Date;
+  toDate?: Date;
+}
+
+interface PaginationOptions {
+  page: number;
+  limit: number;
+}
+
+interface PaginatedResult<T> {
+  data: T[];
+  total: number;
+  page: number;
+  limit: number;
+  totalPages: number;
+}
+
+export interface RecordHistory {
+  changeId: string;
+  operation: OperationType;
+  changedFields: string[] | null;
+  oldData: Record<string, any> | null;
+  newData: Record<string, any> | null;
+  userId: string | null;
+  executedAt: Date;
+}
+
+export class ChangeLogService {
+  private repository: Repository<ChangeLog>;
+
+  constructor(dataSource: DataSource) {
+    this.repository = dataSource.getRepository(ChangeLog);
+  }
+
+  // ============================================
+  // QUERIES
+  // ============================================
+
+  async findAll(
+    tenantId: string,
+    filters: ChangeLogFilters = {},
+    pagination: PaginationOptions = { page: 1, limit: 50 }
+  ): Promise<PaginatedResult<ChangeLog>> {
+    const queryBuilder = this.repository.createQueryBuilder('log')
+      .where('log.tenant_id = :tenantId', { tenantId });
+
+    if (filters.tableSchema) {
+      queryBuilder.andWhere('log.table_schema = :schema', { schema: filters.tableSchema });
+    }
+    if (filters.tableName) {
+      queryBuilder.andWhere('log.table_name = :table', { table: filters.tableName });
+    }
+    if (filters.recordId) {
+      queryBuilder.andWhere('log.record_id = :recordId', { recordId: filters.recordId });
+    }
+    if (filters.userId) {
+      queryBuilder.andWhere('log.user_id = :userId', { userId: filters.userId });
+    }
+    if (filters.operation) {
+      queryBuilder.andWhere('log.operation = :operation', { operation: filters.operation });
+    }
+    if (filters.fromDate) {
+      queryBuilder.andWhere('log.executed_at >= :fromDate', { fromDate: filters.fromDate });
+    }
+    if (filters.toDate) {
+      queryBuilder.andWhere('log.executed_at <= :toDate', { toDate: filters.toDate });
+    }
+
+    const skip = (pagination.page - 1) * pagination.limit;
+
+    const [data, total] = await queryBuilder
+      .orderBy('log.executed_at', 'DESC')
+      .skip(skip)
+      .take(pagination.limit)
+      .getManyAndCount();
+
+    return {
+      data,
+      total,
+      page: pagination.page,
+      limit: pagination.limit,
+      totalPages: Math.ceil(total / pagination.limit),
+    };
+  }
+
+  async findById(id: string): Promise<ChangeLog | null> {
+    return this.repository.findOne({ where: { id } });
+  }
+
+  // ============================================
+  // HISTORIAL DE REGISTRO
+  // ============================================
+
+  async getRecordHistory(
+    tenantId: string,
+    tableSchema: string,
+    tableName: string,
+    recordId: string,
+    limit: number = 100
+  ): Promise<RecordHistory[]> {
+    const logs = await this.repository.find({
+      where: {
+        tenantId,
+        tableSchema,
+        tableName,
+        recordId,
+      },
+      order: { executedAt: 'DESC' },
+      take: limit,
+    });
+
+    return logs.map(log => ({
+      changeId: log.id,
+      operation: log.operation,
+      changedFields: log.changedFields || null,
+      oldData: log.oldData || null,
+      newData: log.newData || null,
+      userId: log.userId || null,
+      executedAt: log.executedAt,
+    }));
+  }
+
+  // ============================================
+  // CAMBIOS RECIENTES
+  // ============================================
+
+  async getRecentChanges(
+    tenantId: string,
+    hours: number = 24,
+    limit: number = 100
+  ): Promise<ChangeLog[]> {
+    const fromDate = new Date();
+    fromDate.setHours(fromDate.getHours() - hours);
+
+    return this.repository.find({
+      where: {
+        tenantId,
+        executedAt: Between(fromDate, new Date()),
+      },
+      order: { executedAt: 'DESC' },
+      take: limit,
+    });
+  }
+
+  async getChangesByUser(
+    tenantId: string,
+    userId: string,
+    pagination: PaginationOptions = { page: 1, limit: 50 }
+  ): Promise<PaginatedResult<ChangeLog>> {
+    return this.findAll(tenantId, { userId }, pagination);
+  }
+
+  async getChangesByTable(
+    tenantId: string,
+    tableSchema: string,
+    tableName: string,
+    pagination: PaginationOptions = { page: 1, limit: 50 }
+  ): Promise<PaginatedResult<ChangeLog>> {
+    return this.findAll(tenantId, { tableSchema, tableName }, pagination);
+  }
+
+  // ============================================
+  // ESTADÍSTICAS
+  // ============================================
+
+  async getStatistics(
+    tenantId: string,
+    fromDate?: Date,
+    toDate?: Date
+  ): Promise<{
+    totalChanges: number;
+    inserts: number;
+    updates: number;
+    deletes: number;
+    tableBreakdown: { schema: string; table: string; count: number }[];
+  }> {
+    const queryBuilder = this.repository.createQueryBuilder('log')
+      .where('log.tenant_id = :tenantId', { tenantId });
+
+    if (fromDate) {
+      queryBuilder.andWhere('log.executed_at >= :fromDate', { fromDate });
+    }
+    if (toDate) {
+      queryBuilder.andWhere('log.executed_at <= :toDate', { toDate });
+    }
+
+    // Counts by operation
+    const [inserts, updates, deletes] = await Promise.all([
+      queryBuilder.clone().andWhere('log.operation = :op', { op: 'INSERT' }).getCount(),
+      queryBuilder.clone().andWhere('log.operation = :op', { op: 'UPDATE' }).getCount(),
+      queryBuilder.clone().andWhere('log.operation = :op', { op: 'DELETE' }).getCount(),
+    ]);
+
+    const totalChanges = inserts + updates + deletes;
+
+    // Table breakdown
+    const tableStats = await this.repository.createQueryBuilder('log')
+      .select('log.table_schema', 'schema')
+      .addSelect('log.table_name', 'table')
+      .addSelect('COUNT(*)', 'count')
+      .where('log.tenant_id = :tenantId', { tenantId })
+      .groupBy('log.table_schema')
+      .addGroupBy('log.table_name')
+      .orderBy('count', 'DESC')
+      .limit(20)
+      .getRawMany();
+
+    return {
+      totalChanges,
+      inserts,
+      updates,
+      deletes,
+      tableBreakdown: tableStats.map(s => ({
+        schema: s.schema,
+        table: s.table,
+        count: parseInt(s.count),
+      })),
+    };
+  }
+
+  // ============================================
+  // MANTENIMIENTO
+  // ============================================
+
+  async purgeOldRecords(tenantId: string, daysToKeep: number = 90): Promise<number> {
+    const cutoffDate = new Date();
+    cutoffDate.setDate(cutoffDate.getDate() - daysToKeep);
+
+    const result = await this.repository.delete({
+      tenantId,
+      executedAt: Between(new Date(0), cutoffDate),
+    });
+
+    return result.affected || 0;
+  }
+}
diff --git a/src/modules/admin/services/index.ts b/src/modules/admin/services/index.ts
index ade2981..acb131d 100644
--- a/src/modules/admin/services/index.ts
+++ b/src/modules/admin/services/index.ts
@@ -7,3 +7,6 @@ export * from './cost-center.service';
 export * from './audit-log.service';
 export * from './system-setting.service';
 export * from './backup.service';
+
+// GAP-007: Audit Triggers
+export * from './change-log.service';
diff --git a/src/modules/documents/controllers/digital-signature.controller.ts b/src/modules/documents/controllers/digital-signature.controller.ts
new file mode 100644
index 0000000..250f2cf
--- /dev/null
+++ b/src/modules/documents/controllers/digital-signature.controller.ts
@@ -0,0 +1,247 @@
+/**
+ * DigitalSignatureController - Controlador de Firmas Digitales
+ *
+ * Endpoints para gestion de firmas digitales de documentos.
+ *
+ * @module Documents (MAE-016)
+ * @gap GAP-006
+ */
+
+import { Router, Request, Response, NextFunction } from 'express';
+import { DataSource } from 'typeorm';
+import { DigitalSignatureService } from '../services';
+
+export function createDigitalSignatureController(dataSource: DataSource): Router {
+  const router = Router();
+  const service = new DigitalSignatureService(dataSource);
+
+  // ==================== CRUD ====================
+
+  /**
+   * GET /
+   * Lista firmas con filtros y paginacion
+   */
+  router.get('/', async (req: Request, res: Response, _next: NextFunction): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+
+      const filters = {
+        documentId: req.query.documentId as string,
+        signerId: req.query.signerId as string,
+        status: req.query.status as any,
+        signatureType: req.query.signatureType as any,
+        fromDate: req.query.fromDate ? new Date(req.query.fromDate as string) : undefined,
+        toDate: req.query.toDate ? new Date(req.query.toDate as string) : undefined,
+      };
+
+      const pagination = {
+        page: parseInt(req.query.page as string) || 1,
+        limit: parseInt(req.query.limit as string) || 20,
+      };
+
+      const result = await service.findAll(tenantId, filters, pagination);
+      res.json(result);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /statistics
+   * Estadisticas de firmas
+   */
+  router.get('/statistics', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const stats = await service.getStatistics(tenantId);
+      res.json(stats);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /pending
+   * Lista firmas pendientes
+   */
+  router.get('/pending', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const signerId = req.query.signerId as string | undefined;
+      const signatures = await service.getPendingSignatures(tenantId, signerId);
+      res.json(signatures);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /by-document/:documentId
+   * Firmas de un documento
+   */
+  router.get('/by-document/:documentId', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const { documentId } = req.params;
+      const signatures = await service.getByDocument(tenantId, documentId);
+      res.json(signatures);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /by-signer/:signerId
+   * Firmas de un firmante
+   */
+  router.get('/by-signer/:signerId', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const { signerId } = req.params;
+      const signatures = await service.getBySigner(tenantId, signerId);
+      res.json(signatures);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * GET /:id
+   * Obtiene firma por ID
+   */
+  router.get('/:id', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const { id } = req.params;
+
+      const signature = await service.findById(tenantId, id);
+      if (!signature) {
+        res.status(404).json({ error: 'Firma no encontrada' });
+        return;
+      }
+      res.json(signature);
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * POST /
+   * Solicita una nueva firma
+   */
+  router.post('/', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const userId = req.headers['x-user-id'] as string;
+
+      const signature = await service.requestSignature(tenantId, req.body, userId);
+      res.status(201).json(signature);
+    } catch (error) {
+      res.status(400).json({ error: (error as Error).message });
+    }
+  });
+
+  // ==================== OPERACIONES ====================
+
+  /**
+   * POST /:id/sign
+   * Firmar documento
+   */
+  router.post('/:id/sign', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const userId = req.headers['x-user-id'] as string;
+      const { id } = req.params;
+
+      // Agregar IP y User-Agent del request
+      const dto = {
+        ...req.body,
+        ipAddress: req.ip || req.headers['x-forwarded-for'],
+        userAgent: req.headers['user-agent'],
+      };
+
+      const signature = await service.signDocument(tenantId, id, dto, userId);
+      if (!signature) {
+        res.status(404).json({ error: 'Firma no encontrada' });
+        return;
+      }
+      res.json(signature);
+    } catch (error) {
+      res.status(400).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * POST /:id/reject
+   * Rechazar solicitud de firma
+   */
+  router.post('/:id/reject', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const userId = req.headers['x-user-id'] as string;
+      const { id } = req.params;
+
+      const signature = await service.rejectSignature(tenantId, id, req.body, userId);
+      if (!signature) {
+        res.status(404).json({ error: 'Firma no encontrada' });
+        return;
+      }
+      res.json(signature);
+    } catch (error) {
+      res.status(400).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * POST /:id/revoke
+   * Revocar firma
+   */
+  router.post('/:id/revoke', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const userId = req.headers['x-user-id'] as string;
+      const { id } = req.params;
+
+      const signature = await service.revokeSignature(tenantId, id, req.body.reason, userId);
+      if (!signature) {
+        res.status(404).json({ error: 'Firma no encontrada' });
+        return;
+      }
+      res.json(signature);
+    } catch (error) {
+      res.status(400).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * POST /:id/validate
+   * Validar firma
+   */
+  router.post('/:id/validate', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const { id } = req.params;
+
+      const result = await service.validateSignature(tenantId, id);
+      res.json(result);
+    } catch (error) {
+      res.status(400).json({ error: (error as Error).message });
+    }
+  });
+
+  /**
+   * POST /mark-expired
+   * Marcar firmas expiradas (job interno)
+   */
+  router.post('/mark-expired', async (req: Request, res: Response): Promise<void> => {
+    try {
+      const tenantId = req.headers['x-tenant-id'] as string;
+      const count = await service.markExpiredSignatures(tenantId);
+      res.json({ marked: count });
+    } catch (error) {
+      res.status(500).json({ error: (error as Error).message });
+    }
+  });
+
+  return router;
+}
diff --git a/src/modules/documents/controllers/index.ts b/src/modules/documents/controllers/index.ts
index 2f16959..efc00b1 100644
--- a/src/modules/documents/controllers/index.ts
+++ b/src/modules/documents/controllers/index.ts
@@ -4,3 +4,6 @@
  */
 
 export * from './document.controller';
+
+// GAP-006: Firmas Digitales
+export * from './digital-signature.controller';
diff --git a/src/modules/documents/entities/digital-signature.entity.ts b/src/modules/documents/entities/digital-signature.entity.ts
new file mode 100644
index 0000000..5fa9247
--- /dev/null
+++ b/src/modules/documents/entities/digital-signature.entity.ts
@@ -0,0 +1,152 @@
+/**
+ * DigitalSignature Entity
+ *
+ * Firmas digitales para documentos con soporte para
+ * firma simple, avanzada y cualificada.
+ *
+ * @module Documents (MAE-016)
+ * @table documents.digital_signatures
+ * @gap GAP-006
+ */
+
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  CreateDateColumn,
+  UpdateDateColumn,
+  ManyToOne,
+  JoinColumn,
+  Index,
+} from 'typeorm';
+import { Tenant } from '../../core/entities/tenant.entity';
+
+export type SignatureType = 'simple' | 'advanced' | 'qualified';
+
+export type SignatureStatus = 'pending' | 'signed' | 'rejected' | 'expired' | 'revoked';
+
+@Entity({ schema: 'documents', name: 'digital_signatures' })
+@Index(['tenantId'])
+@Index(['documentId'])
+@Index(['signerId'])
+@Index(['tenantId', 'status'])
+@Index(['signedAt'])
+export class DigitalSignature {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ name: 'tenant_id', type: 'uuid' })
+  tenantId!: string;
+
+  // Documento
+  @Column({ name: 'document_id', type: 'uuid' })
+  documentId!: string;
+
+  @Column({ name: 'version_id', type: 'uuid', nullable: true })
+  versionId?: string;
+
+  // Firmante
+  @Column({ name: 'signer_id', type: 'uuid' })
+  signerId!: string;
+
+  @Column({ name: 'signer_name', length: 200 })
+  signerName!: string;
+
+  @Column({ name: 'signer_email', length: 255, nullable: true })
+  signerEmail?: string;
+
+  @Column({ name: 'signer_role', length: 100, nullable: true })
+  signerRole?: string;
+
+  // Tipo y estado
+  @Column({
+    name: 'signature_type',
+    type: 'varchar',
+    length: 20,
+    default: 'simple',
+  })
+  signatureType!: SignatureType;
+
+  @Column({
+    type: 'varchar',
+    length: 20,
+    default: 'pending',
+  })
+  status!: SignatureStatus;
+
+  // Datos de firma
+  @Column({ name: 'signature_data', type: 'text', nullable: true })
+  signatureData?: string;
+
+  @Column({ name: 'signature_hash', length: 128, nullable: true })
+  signatureHash?: string;
+
+  @Column({ name: 'hash_algorithm', length: 20, default: 'SHA-256' })
+  hashAlgorithm!: string;
+
+  // Certificado
+  @Column({ name: 'certificate_info', type: 'jsonb', nullable: true })
+  certificateInfo?: Record<string, any>;
+
+  @Column({ name: 'certificate_serial', length: 100, nullable: true })
+  certificateSerial?: string;
+
+  @Column({ name: 'certificate_issuer', length: 255, nullable: true })
+  certificateIssuer?: string;
+
+  @Column({ name: 'certificate_valid_from', type: 'timestamptz', nullable: true })
+  certificateValidFrom?: Date;
+
+  @Column({ name: 'certificate_valid_to', type: 'timestamptz', nullable: true })
+  certificateValidTo?: Date;
+
+  // Timestamps
+  @Column({ name: 'requested_at', type: 'timestamptz', default: () => 'NOW()' })
+  requestedAt!: Date;
+
+  @Column({ name: 'signed_at', type: 'timestamptz', nullable: true })
+  signedAt?: Date;
+
+  @Column({ name: 'expires_at', type: 'timestamptz', nullable: true })
+  expiresAt?: Date;
+
+  // Contexto
+  @Column({ name: 'ip_address', type: 'inet', nullable: true })
+  ipAddress?: string;
+
+  @Column({ name: 'user_agent', type: 'text', nullable: true })
+  userAgent?: string;
+
+  @Column({ type: 'jsonb', nullable: true })
+  geolocation?: Record<string, any>;
+
+  // Validación
+  @Column({ name: 'is_valid', type: 'boolean', default: true })
+  isValid!: boolean;
+
+  @Column({ name: 'validation_errors', type: 'jsonb', nullable: true })
+  validationErrors?: Record<string, any>;
+
+  @Column({ name: 'last_validated_at', type: 'timestamptz', nullable: true })
+  lastValidatedAt?: Date;
+
+  // Razón
+  @Column({ type: 'text', nullable: true })
+  reason?: string;
+
+  // Metadatos
+  @Column({ type: 'jsonb', default: '{}' })
+  metadata!: Record<string, any>;
+
+  // Relaciones
+  @ManyToOne(() => Tenant)
+  @JoinColumn({ name: 'tenant_id' })
+  tenant?: Tenant;
+
+  // Auditoría
+  @CreateDateColumn({ name: 'created_at', type: 'timestamptz' })
+  createdAt!: Date;
+
+  @UpdateDateColumn({ name: 'updated_at', type: 'timestamptz' })
+  updatedAt!: Date;
+}
diff --git a/src/modules/documents/entities/index.ts b/src/modules/documents/entities/index.ts
index 622807f..d232b12 100644
--- a/src/modules/documents/entities/index.ts
+++ b/src/modules/documents/entities/index.ts
@@ -14,3 +14,6 @@ export * from './approval-action.entity';
 export * from './annotation.entity';
 export * from './access-log.entity';
 export * from './document-share.entity';
+
+// GAP-006: Firmas Digitales
+export * from './digital-signature.entity';
diff --git a/src/modules/documents/services/digital-signature.service.ts b/src/modules/documents/services/digital-signature.service.ts
new file mode 100644
index 0000000..4164439
--- /dev/null
+++ b/src/modules/documents/services/digital-signature.service.ts
@@ -0,0 +1,339 @@
+/**
+ * Digital Signature Service
+ * ERP Construccion - Modulo Documents (MAE-016)
+ *
+ * Logica de negocio para firmas digitales de documentos.
+ * @gap GAP-006
+ */
+
+import { Repository, DataSource, LessThan } from 'typeorm';
+import { DigitalSignature, SignatureType, SignatureStatus } from '../entities/digital-signature.entity';
+import * as crypto from 'crypto';
+
+// DTOs
+export interface CreateSignatureRequestDto {
+  documentId: string;
+  versionId?: string;
+  signerId: string;
+  signerName: string;
+  signerEmail?: string;
+  signerRole?: string;
+  signatureType?: SignatureType;
+  expiresAt?: Date;
+  metadata?: Record<string, any>;
+}
+
+export interface SignDocumentDto {
+  signatureData?: string;
+  certificateInfo?: Record<string, any>;
+  certificateSerial?: string;
+  certificateIssuer?: string;
+  ipAddress?: string;
+  userAgent?: string;
+  geolocation?: Record<string, any>;
+}
+
+export interface RejectSignatureDto {
+  reason: string;
+}
+
+export interface SignatureFilters {
+  documentId?: string;
+  signerId?: string;
+  status?: SignatureStatus;
+  signatureType?: SignatureType;
+  fromDate?: Date;
+  toDate?: Date;
+}
+
+interface PaginationOptions {
+  page: number;
+  limit: number;
+}
+
+interface PaginatedResult<T> {
+  data: T[];
+  total: number;
+  page: number;
+  limit: number;
+  totalPages: number;
+}
+
+export class DigitalSignatureService {
+  private repository: Repository<DigitalSignature>;
+
+  constructor(dataSource: DataSource) {
+    this.repository = dataSource.getRepository(DigitalSignature);
+  }
+
+  // ============================================
+  // CRUD
+  // ============================================
+
+  async requestSignature(
+    tenantId: string,
+    dto: CreateSignatureRequestDto,
+    _userId?: string
+  ): Promise<DigitalSignature> {
+    const signature = this.repository.create({
+      tenantId,
+      documentId: dto.documentId,
+      versionId: dto.versionId,
+      signerId: dto.signerId,
+      signerName: dto.signerName,
+      signerEmail: dto.signerEmail,
+      signerRole: dto.signerRole,
+      signatureType: dto.signatureType || 'simple',
+      status: 'pending',
+      expiresAt: dto.expiresAt,
+      metadata: dto.metadata || {},
+      requestedAt: new Date(),
+    });
+
+    return this.repository.save(signature);
+  }
+
+  async findById(tenantId: string, id: string): Promise<DigitalSignature | null> {
+    return this.repository.findOne({
+      where: { id, tenantId },
+    });
+  }
+
+  async findAll(
+    tenantId: string,
+    filters: SignatureFilters = {},
+    pagination: PaginationOptions = { page: 1, limit: 20 }
+  ): Promise<PaginatedResult<DigitalSignature>> {
+    const queryBuilder = this.repository.createQueryBuilder('sig')
+      .where('sig.tenant_id = :tenantId', { tenantId });
+
+    if (filters.documentId) {
+      queryBuilder.andWhere('sig.document_id = :documentId', { documentId: filters.documentId });
+    }
+    if (filters.signerId) {
+      queryBuilder.andWhere('sig.signer_id = :signerId', { signerId: filters.signerId });
+    }
+    if (filters.status) {
+      queryBuilder.andWhere('sig.status = :status', { status: filters.status });
+    }
+    if (filters.signatureType) {
+      queryBuilder.andWhere('sig.signature_type = :type', { type: filters.signatureType });
+    }
+    if (filters.fromDate) {
+      queryBuilder.andWhere('sig.requested_at >= :fromDate', { fromDate: filters.fromDate });
+    }
+    if (filters.toDate) {
+      queryBuilder.andWhere('sig.requested_at <= :toDate', { toDate: filters.toDate });
+    }
+
+    const skip = (pagination.page - 1) * pagination.limit;
+
+    const [data, total] = await queryBuilder
+      .orderBy('sig.requested_at', 'DESC')
+      .skip(skip)
+      .take(pagination.limit)
+      .getManyAndCount();
+
+    return {
+      data,
+      total,
+      page: pagination.page,
+      limit: pagination.limit,
+      totalPages: Math.ceil(total / pagination.limit),
+    };
+  }
+
+  // ============================================
+  // OPERACIONES DE FIRMA
+  // ============================================
+
+  async signDocument(
+    tenantId: string,
+    id: string,
+    dto: SignDocumentDto,
+    _userId?: string
+  ): Promise<DigitalSignature | null> {
+    const signature = await this.findById(tenantId, id);
+    if (!signature) return null;
+
+    if (signature.status !== 'pending') {
+      throw new Error('Signature request is not pending');
+    }
+
+    // Check expiration
+    if (signature.expiresAt && signature.expiresAt < new Date()) {
+      signature.status = 'expired';
+      await this.repository.save(signature);
+      throw new Error('Signature request has expired');
+    }
+
+    // Generate signature hash
+    const dataToHash = JSON.stringify({
+      documentId: signature.documentId,
+      signerId: signature.signerId,
+      timestamp: new Date().toISOString(),
+      signatureData: dto.signatureData,
+    });
+    const signatureHash = crypto.createHash('sha256').update(dataToHash).digest('hex');
+
+    signature.signatureData = dto.signatureData;
+    signature.signatureHash = signatureHash;
+    signature.certificateInfo = dto.certificateInfo;
+    signature.certificateSerial = dto.certificateSerial;
+    signature.certificateIssuer = dto.certificateIssuer;
+    signature.ipAddress = dto.ipAddress;
+    signature.userAgent = dto.userAgent;
+    signature.geolocation = dto.geolocation;
+    signature.signedAt = new Date();
+    signature.status = 'signed';
+    signature.isValid = true;
+    signature.lastValidatedAt = new Date();
+
+    return this.repository.save(signature);
+  }
+
+  async rejectSignature(
+    tenantId: string,
+    id: string,
+    dto: RejectSignatureDto,
+    _userId?: string
+  ): Promise<DigitalSignature | null> {
+    const signature = await this.findById(tenantId, id);
+    if (!signature) return null;
+
+    if (signature.status !== 'pending') {
+      throw new Error('Signature request is not pending');
+    }
+
+    signature.status = 'rejected';
+    signature.reason = dto.reason;
+
+    return this.repository.save(signature);
+  }
+
+  async revokeSignature(
+    tenantId: string,
+    id: string,
+    reason: string,
+    _userId?: string
+  ): Promise<DigitalSignature | null> {
+    const signature = await this.findById(tenantId, id);
+    if (!signature) return null;
+
+    if (signature.status !== 'signed') {
+      throw new Error('Only signed documents can be revoked');
+    }
+
+    signature.status = 'revoked';
+    signature.reason = reason;
+    signature.isValid = false;
+
+    return this.repository.save(signature);
+  }
+
+  async validateSignature(
+    tenantId: string,
+    id: string
+  ): Promise<{ isValid: boolean; errors?: string[] }> {
+    const signature = await this.findById(tenantId, id);
+    if (!signature) {
+      return { isValid: false, errors: ['Signature not found'] };
+    }
+
+    const errors: string[] = [];
+
+    // Check status
+    if (signature.status !== 'signed') {
+      errors.push(`Invalid status: ${signature.status}`);
+    }
+
+    // Check certificate validity for advanced/qualified signatures
+    if (signature.signatureType !== 'simple' && signature.certificateValidTo) {
+      if (signature.certificateValidTo < new Date()) {
+        errors.push('Certificate has expired');
+      }
+    }
+
+    // Update validation timestamp
+    signature.lastValidatedAt = new Date();
+    signature.validationErrors = errors.length > 0 ? { errors } : undefined;
+    signature.isValid = errors.length === 0;
+    await this.repository.save(signature);
+
+    return {
+      isValid: errors.length === 0,
+      errors: errors.length > 0 ? errors : undefined,
+    };
+  }
+
+  // ============================================
+  // QUERIES
+  // ============================================
+
+  async getByDocument(tenantId: string, documentId: string): Promise<DigitalSignature[]> {
+    return this.repository.find({
+      where: { tenantId, documentId },
+      order: { requestedAt: 'DESC' },
+    });
+  }
+
+  async getBySigner(tenantId: string, signerId: string): Promise<DigitalSignature[]> {
+    return this.repository.find({
+      where: { tenantId, signerId },
+      order: { requestedAt: 'DESC' },
+    });
+  }
+
+  async getPendingSignatures(tenantId: string, signerId?: string): Promise<DigitalSignature[]> {
+    const where: any = { tenantId, status: 'pending' as SignatureStatus };
+    if (signerId) {
+      where.signerId = signerId;
+    }
+
+    return this.repository.find({
+      where,
+      order: { requestedAt: 'ASC' },
+    });
+  }
+
+  async getExpiredSignatures(tenantId: string): Promise<DigitalSignature[]> {
+    return this.repository.find({
+      where: {
+        tenantId,
+        status: 'pending' as SignatureStatus,
+        expiresAt: LessThan(new Date()),
+      },
+    });
+  }
+
+  async markExpiredSignatures(tenantId: string): Promise<number> {
+    const result = await this.repository.update(
+      {
+        tenantId,
+        status: 'pending' as SignatureStatus,
+        expiresAt: LessThan(new Date()),
+      },
+      { status: 'expired' as SignatureStatus }
+    );
+
+    return result.affected || 0;
+  }
+
+  async getStatistics(tenantId: string): Promise<{
+    pending: number;
+    signed: number;
+    rejected: number;
+    expired: number;
+    revoked: number;
+  }> {
+    const [pending, signed, rejected, expired, revoked] = await Promise.all([
+      this.repository.count({ where: { tenantId, status: 'pending' } }),
+      this.repository.count({ where: { tenantId, status: 'signed' } }),
+      this.repository.count({ where: { tenantId, status: 'rejected' } }),
+      this.repository.count({ where: { tenantId, status: 'expired' } }),
+      this.repository.count({ where: { tenantId, status: 'revoked' } }),
+    ]);
+
+    return { pending, signed, rejected, expired, revoked };
+  }
+}
diff --git a/src/modules/documents/services/index.ts b/src/modules/documents/services/index.ts
index 80ff157..f8595f9 100644
--- a/src/modules/documents/services/index.ts
+++ b/src/modules/documents/services/index.ts
@@ -5,3 +5,6 @@
 
 export * from './document.service';
 export * from './document-version.service';
+
+// GAP-006: Firmas Digitales
+export * from './digital-signature.service';
diff --git a/src/server.ts b/src/server.ts
index 929eebd..238b37c 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -62,8 +62,10 @@ import { createComparativoController } from './modules/purchase/controllers';
 import { createDerechohabienteController, createAsignacionController } from './modules/infonavit/controllers';
 import { createInspectionController, createTicketController } from './modules/quality/controllers';
 import { createContractController, createSubcontractorController } from './modules/contracts/controllers';
-import { createReportController, createDashboardController, createKpiController } from './modules/reports/controllers';
-import { createCostCenterController, createAuditLogController, createSystemSettingController, createBackupController } from './modules/admin/controllers';
+import { createReportController, createDashboardController, createKpiController, createKpiConfigController } from './modules/reports/controllers';
+import { createToolLoanController, createDepreciationController } from './modules/assets/controllers';
+import { createCostCenterController, createAuditLogController, createSystemSettingController, createBackupController, createChangeLogController } from './modules/admin/controllers';
+import { createDigitalSignatureController } from './modules/documents/controllers';
 import { createOpportunityController, createBidAnalyticsController, createTenderController, createProposalController, createVendorController } from './modules/bidding/controllers';
 import { createAccountingController, createAPController, createARController, createCashFlowController, createBankReconciliationController, createReportsController } from './modules/finance/controllers';
 
@@ -124,6 +126,13 @@ app.get(`/api/${API_VERSION}`, (_req, res) => {
       'payment-terminals': `/api/${API_VERSION}/payment-terminals`,
       mercadopago: `/api/${API_VERSION}/mercadopago`,
       clip: `/api/${API_VERSION}/clip`,
+      // GAP-001, GAP-002, GAP-003
+      'kpis-config': `/api/${API_VERSION}/kpis-config`,
+      'tool-loans': `/api/${API_VERSION}/tool-loans`,
+      depreciation: `/api/${API_VERSION}/depreciation`,
+      // GAP-006, GAP-007
+      'digital-signatures': `/api/${API_VERSION}/digital-signatures`,
+      'change-log': `/api/${API_VERSION}/change-log`,
     },
   });
 });
@@ -136,26 +145,7 @@ app.use(`/api/${API_VERSION}/fraccionamientos`, fraccionamientoController);
 let authController: ReturnType<typeof createAuthController>;
 let usersController: ReturnType<typeof createUsersController>;
 
-/**
- * 404 Handler
- */
-app.use((req, res) => {
-  res.status(404).json({
-    error: 'Not Found',
-    message: `Cannot ${req.method} ${req.path}`,
-  });
-});
-
-/**
- * Error Handler
- */
-app.use((err: Error, _req: express.Request, res: express.Response, _next: express.NextFunction) => {
-  console.error('Error:', err);
-  res.status(500).json({
-    error: 'Internal Server Error',
-    message: process.env.NODE_ENV === 'development' ? err.message : 'Something went wrong',
-  });
-});
+// 404 and Error handlers are registered in bootstrap() after all routes
 
 /**
  * Inicializar Base de Datos y Servidor
@@ -357,6 +347,44 @@ async function bootstrap() {
     app.use('/webhooks', paymentTerminals.webhookRouter);
     console.log('💳 Payment Terminals module inicializado');
 
+    // Inicializar GAP Controllers (KPIs, Tool Loans, Depreciation)
+    const kpiConfigController = createKpiConfigController(AppDataSource);
+    app.use(`/api/${API_VERSION}/kpis-config`, kpiConfigController);
+
+    const toolLoanController = createToolLoanController(AppDataSource);
+    app.use(`/api/${API_VERSION}/tool-loans`, toolLoanController);
+
+    const depreciationController = createDepreciationController(AppDataSource);
+    app.use(`/api/${API_VERSION}/depreciation`, depreciationController);
+
+    console.log('🔧 GAP modules inicializados (KPIs Config, Tool Loans, Depreciation)');
+
+    // Inicializar GAP-006 y GAP-007 Controllers
+    const digitalSignatureController = createDigitalSignatureController(AppDataSource);
+    app.use(`/api/${API_VERSION}/digital-signatures`, digitalSignatureController);
+
+    const changeLogController = createChangeLogController(AppDataSource);
+    app.use(`/api/${API_VERSION}/change-log`, changeLogController);
+
+    console.log('🔐 GAP modules inicializados (Digital Signatures, Change Log)');
+
+    // 404 Handler - MUST be after all routes
+    app.use((req, res) => {
+      res.status(404).json({
+        error: 'Not Found',
+        message: `Cannot ${req.method} ${req.path}`,
+      });
+    });
+
+    // Error Handler - MUST be last
+    app.use((err: Error, _req: express.Request, res: express.Response, _next: express.NextFunction) => {
+      console.error('Error:', err);
+      res.status(500).json({
+        error: 'Internal Server Error',
+        message: process.env.NODE_ENV === 'development' ? err.message : 'Something went wrong',
+      });
+    });
+
     // Iniciar servidor
     app.listen(PORT, () => {
       console.log('🚀 Servidor iniciado');