Complete Step 1.1: ValidatePDF Application Layer

Updated PHASENPLAN and ROADMAP to reflect progress on Feature 1 - ValidatePDF (75% complete). Marked Step 1.1 as completed, including MediatR setup, pipeline behaviors (`ValidationBehavior`, `LoggingBehavior`), ValidatePDF feature (Query, Handler, Validator), and DTOs.

Added `DependencyInjection.cs` for Application Layer DI configuration. Introduced `LoggingBehavior` and `ValidationBehavior` for MediatR pipelines. Implemented `ValidatePdfHandler`, `ValidatePdfQuery`, and `ValidatePdfValidator`.

Created DTOs (`ValidatePdfRequest`, `ValidatePdfResponse`) for the ValidatePDF feature. Added unit tests for `ValidatePdfHandler` to verify metadata handling and exception propagation.

Removed unused folder references in `DocumentOperator.Application.csproj`.

DocumentOperator.API/PHASENPLAN.md

@@ -1,6 +1,6 @@
 # ?? DocumentOperator - Phasenplan (Feature-Driven Development)
 
-> **Stand:** 17.01.2025 | **Aktuell:** Feature 1 - ValidatePDF (Step 1.1 NEXT) | **Projektdauer:** 6 Wochen
+> **Stand:** 17.01.2025 | **Aktuell:** Feature 1 - ValidatePDF (Step 1.2 NEXT) | **Projektdauer:** 6 Wochen
 
 ---
 
@@ -8,7 +8,7 @@
 
 | Woche | Features / Concerns | Status | Fortschritt |
 |-------|---------------------|--------|-------------|
-| **W1** | Feature 1: ValidatePDF | ?? In Progress | 50% (Infrastructure fertig, Application NEXT) |
+| **W1** | Feature 1: ValidatePDF | ?? In Progress | 75% (Foundation + Application fertig, API NEXT) |
 | **W2** | Feature 2: ExtractAttachments | ? Geplant | 0% |
 | **W2** | Feature 3: ApplyStamp | ? Geplant | 0% |
 | **W3** | Feature 4: EmbedCertificate | ? Geplant | 0% |
@@ -42,7 +42,7 @@
 
 ## ?? DETAILLIERTER PLAN
 
-### WOCHE 1 - Feature 1: ValidatePDF | ?? In Progress - 50%
+### WOCHE 1 - Feature 1: ValidatePDF | ?? In Progress - 75%
 
 **Ziel:** POST /api/v1/documents/validate Endpoint im Swagger testbar
 
@@ -58,38 +58,38 @@
 
 ---
 
-#### ?? Step 1.1: Application Layer (MediatR Setup + ValidatePDF Feature) - **NEXT**
+#### ? Step 1.1: Application Layer (MediatR Setup + ValidatePDF Feature) - **ABGESCHLOSSEN**
 **Dauer:** ~4 Stunden
-**Status:** ? NEXT
+**Status:** ? ABGESCHLOSSEN
 
-**Was wird erstellt:**
+**Was wurde erstellt:**
 1. **MediatR Setup**
-   - `Application/DependencyInjection.cs` (Service Registration)
+   - ? `Application/DependencyInjection.cs` (Service Registration)
-   - `Application/Common/Behaviors/ValidationBehavior.cs` (FluentValidation Pipeline)
+   - ? `Application/Common/Behaviors/ValidationBehavior.cs` (FluentValidation Pipeline)
-   - `Application/Common/Behaviors/LoggingBehavior.cs` (Logging Pipeline)
+   - ? `Application/Common/Behaviors/LoggingBehavior.cs` (Logging Pipeline mit ILogger<T>)
 
 2. **ValidatePDF Feature (Vertical Slice)**
-   - `Application/Features/Documents/ValidatePdf/ValidatePdfQuery.cs`
+   - ? `Application/Features/Documents/ValidatePdf/ValidatePdfQuery.cs`
-   - `Application/Features/Documents/ValidatePdf/ValidatePdfHandler.cs`
+   - ? `Application/Features/Documents/ValidatePdf/ValidatePdfHandler.cs`
-   - `Application/Features/Documents/ValidatePdf/ValidatePdfValidator.cs`
+   - ? `Application/Features/Documents/ValidatePdf/ValidatePdfValidator.cs`
 
 3. **DTOs**
-   - `Application/Common/DTOs/ValidatePdfRequest.cs`
+   - ? `Application/Common/DTOs/ValidatePdfRequest.cs`
-   - `Application/Common/DTOs/ValidatePdfResponse.cs`
+   - ? `Application/Common/DTOs/ValidatePdfResponse.cs`
 
 4. **Tests**
-   - `Tests/Unit/Application/Features/ValidatePdf/ValidatePdfHandlerTests.cs`
+   - ? `Tests/Unit/Application/Features/ValidatePdf/ValidatePdfHandlerTests.cs` (2 Tests - alle grün!)
 
 **Akzeptanzkriterien:**
 - ? Build erfolgreich
-- ? Tests grün (Handler Tests)
+- ? Tests grün (Handler Tests: 2/2 passed)
 - ? MediatR Pipeline funktioniert (Validation + Logging)
 
 ---
 
-#### ? Step 1.2: API Layer (Endpoint + Exception Middleware)
+#### ?? Step 1.2: API Layer (Endpoint + Exception Middleware) - **NEXT**
 **Dauer:** ~3 Stunden
-**Status:** ? Pending
+**Status:** ? NEXT
 
 **Was wird erstellt:**
 1. **Exception Middleware**
@@ -418,7 +418,7 @@
 | Kategorie | Status | Fortschritt |
 |-----------|--------|-------------|
 | **Foundation** | ? Abgeschlossen | 100% |
-| **Feature 1** | ?? In Progress | 50% |
+| **Feature 1** | ?? In Progress | 75% |
 | **Feature 2-5** | ? Pending | 0% |
 | **Multi-Tenancy** | ? Pending | 0% |
 | **Cross-Cutting** | ? Pending | 0% |
@@ -430,19 +430,19 @@
 
 ### Heute (17.01.2025)
 
-**Feature 1 - Step 1.1: Application Layer**
+**Feature 1 - Step 1.1: Application Layer** ? **ABGESCHLOSSEN**
 1. ? MediatR Setup (DependencyInjection.cs)
 2. ? ValidationBehavior.cs erstellen
-3. ? LoggingBehavior.cs erstellen
+3. ? LoggingBehavior.cs erstellen (mit ILogger<T>)
 4. ? ValidatePDF Feature erstellen (Query, Handler, Validator)
 5. ? DTOs erstellen (Request, Response)
-6. ? Tests schreiben (ValidatePdfHandlerTests.cs)
+6. ? Tests schreiben (ValidatePdfHandlerTests.cs - 2 Tests grün)
 7. ? Build + Tests grün
 8. ? ROADMAP + PHASENPLAN aktualisieren
 9. ? Commit
 
 **Danach:**
-? Feature 1 - Step 1.2: API Layer (Endpoint + Exception Middleware)
+? Feature 1 - Step 1.2: API Layer (Endpoint + Exception Middleware) - **NEXT**
 
 ---
 
@@ -455,6 +455,7 @@
 | 17.01.2025 | Infrastructure | DevExpressPdfProcessor.ValidateAsync implementiert |
 | 17.01.2025 | Tests | DevExpressPdfProcessorTests.cs erstellt (6 Tests) |
 | 17.01.2025 | **PHASENPLAN** | ?? **Komplett umstrukturiert** (Feature-basiert + Datum korrigiert 23.06.2026 ? 17.01.2025) |
+| 17.01.2025 | **Feature 1 - Step 1.1** | ? **ABGESCHLOSSEN** - Application Layer (MediatR, Behaviors, ValidatePDF Feature, DTOs, Tests - 2/2 grün) |
 
 ---
 

DocumentOperator.API/ROADMAP.md

@@ -1,6 +1,6 @@
 # ?? DocumentOperator - Project Roadmap (Feature-Driven Development)
 
-> **Last Updated:** 17.01.2025 | **Status:** In Development | **Current Feature:** Feature 1 - ValidatePDF (NEXT)
+> **Last Updated:** 17.01.2025 | **Status:** In Development | **Current Feature:** Feature 1 - ValidatePDF (Step 1.2 NEXT)
 
 ---
 
@@ -44,7 +44,7 @@
 
 | Feature | Type | Status | Swagger Testbar? |
 |---------|------|--------|------------------|
-| **1. ValidatePDF** | Synchron | ?? NEXT | ? |
+| **1. ValidatePDF** | Synchron | ?? In Progress (Step 1.2 NEXT) | ? |
 | **2. ExtractAttachments** | Synchron | ? Pending | ? |
 | **3. ApplyStamp** | Synchron | ? Pending | ? |
 | **4. EmbedCertificate** | Synchron | ? Pending | ? |
@@ -61,7 +61,7 @@
 
 ---
 
-## ?? FEATURE 1: ValidatePDF (Synchron) - **NEXT**
+## ?? FEATURE 1: ValidatePDF (Synchron) - **In Progress**
 
 **Was macht dieses Feature?**
 - Client sendet PDF als Base64 (JSON)
@@ -77,7 +77,7 @@ Response: { "pageCount": 5, "fileSizeBytes": 1024, "pdfVersion": "1.4", "hasAtta
 
 ---
 
-### ? Step 1.0: Foundation (bereits erledigt!)
+### ? Step 1.0: Foundation (ABGESCHLOSSEN)
 
 **Was wurde bereits erstellt:**
 - ? Domain Layer (Exceptions, Enums, Value Objects)
@@ -92,36 +92,36 @@ Response: { "pageCount": 5, "fileSizeBytes": 1024, "pdfVersion": "1.4", "hasAtta
 
 ---
 
-### ?? Step 1.1: Application Layer (MediatR Setup + ValidatePDF Feature) - **NEXT**
+### ? Step 1.1: Application Layer (MediatR Setup + ValidatePDF Feature) - **ABGESCHLOSSEN**
 
 **Ziel:** MediatR + FluentValidation + ValidatePDF Handler
 
-**Was wird erstellt:**
+**Was wurde erstellt:**
 
 #### 1.1.1: MediatR Setup
-- **Datei:** `Application/DependencyInjection.cs`
+- ? **Datei:** `Application/DependencyInjection.cs`
   - Registriert MediatR
   - Registriert FluentValidation
   - Registriert Pipeline Behaviors (Validation + Logging)
 
 #### 1.1.2: Pipeline Behaviors
-- **Datei:** `Application/Common/Behaviors/ValidationBehavior.cs`
+- ? **Datei:** `Application/Common/Behaviors/ValidationBehavior.cs`
   - Führt FluentValidation automatisch aus (vor jedem Handler)
   - Wirft `ValidationException` bei Fehler
 
-- **Datei:** `Application/Common/Behaviors/LoggingBehavior.cs`
+- ? **Datei:** `Application/Common/Behaviors/LoggingBehavior.cs`
   - Loggt jeden Request (mit Performance-Tracking)
-  - Nutzt Serilog
+  - Nutzt `ILogger<T>` (Clean Architecture konform!)
 
 #### 1.1.3: ValidatePDF Feature (Vertical Slice)
-- **Ordner:** `Application/Features/Documents/ValidatePdf/`
+- ? **Ordner:** `Application/Features/Documents/ValidatePdf/`
 
-- **Datei:** `ValidatePdfQuery.cs`
+- ? **Datei:** `ValidatePdfQuery.cs`
   ```csharp
   public record ValidatePdfQuery(Base64String PdfContent) : IRequest<PdfMetadata>;
   ```
 
-- **Datei:** `ValidatePdfHandler.cs`
+- ? **Datei:** `ValidatePdfHandler.cs`
   ```csharp
   public class ValidatePdfHandler : IRequestHandler<ValidatePdfQuery, PdfMetadata>
   {
@@ -135,7 +135,7 @@ Response: { "pageCount": 5, "fileSizeBytes": 1024, "pdfVersion": "1.4", "hasAtta
   }
   ```
 
-- **Datei:** `ValidatePdfValidator.cs`
+- ? **Datei:** `ValidatePdfValidator.cs`
   ```csharp
   public class ValidatePdfValidator : AbstractValidator<ValidatePdfQuery>
   {
@@ -147,14 +147,14 @@ Response: { "pageCount": 5, "fileSizeBytes": 1024, "pdfVersion": "1.4", "hasAtta
   ```
 
 #### 1.1.4: DTOs
-- **Ordner:** `Application/Common/DTOs/`
+- ? **Ordner:** `Application/Common/DTOs/`
 
-- **Datei:** `ValidatePdfRequest.cs`
+- ? **Datei:** `ValidatePdfRequest.cs`
   ```csharp
   public record ValidatePdfRequest(string Base64Pdf);
   ```
 
-- **Datei:** `ValidatePdfResponse.cs`
+- ? **Datei:** `ValidatePdfResponse.cs`
   ```csharp
   public record ValidatePdfResponse(
       int PageCount,
@@ -166,9 +166,9 @@ Response: { "pageCount": 5, "fileSizeBytes": 1024, "pdfVersion": "1.4", "hasAtta
   ```
 
 #### 1.1.5: Tests
-- **Datei:** `Tests/Unit/Application/Features/ValidatePdf/ValidatePdfHandlerTests.cs`
+- ? **Datei:** `Tests/Unit/Application/Features/ValidatePdf/ValidatePdfHandlerTests.cs`
-  - Test: `Handle_ValidPdf_ReturnsPdfMetadata`
+  - ? Test: `Handle_ValidPdf_ReturnsPdfMetadata`
-  - Test: `Handle_NullPdfContent_ThrowsValidationException`
+  - ? Test: `Handle_PdfProcessorThrowsException_PropagatesException`
 
 **Akzeptanzkriterien:**
 - ? Build erfolgreich
@@ -177,7 +177,7 @@ Response: { "pageCount": 5, "fileSizeBytes": 1024, "pdfVersion": "1.4", "hasAtta
 
 ---
 
-### ?? Step 1.2: API Layer (Endpoint + Exception Middleware)
+### ?? Step 1.2: API Layer (Endpoint + Exception Middleware) - **NEXT**
 
 **Ziel:** HTTP Endpoint + zentrale Exception Handling
 
@@ -898,10 +898,18 @@ DocumentOperator.Tests/
   - ? IPdfProcessor Interface
   - ? DevExpressPdfProcessor.ValidateAsync (mit Tests!)
 
+- **Application Layer:**
+  - ? DependencyInjection.cs (MediatR + FluentValidation)
+  - ? ValidationBehavior.cs (FluentValidation Pipeline)
+  - ? LoggingBehavior.cs (ILogger<T> Pipeline)
+  - ? ValidatePDF Feature (Query, Handler, Validator)
+  - ? DTOs (ValidatePdfRequest, ValidatePdfResponse)
+  - ? Tests (ValidatePdfHandlerTests - 2 Tests grün)
+
 ### ?? In Progress
 
 - **Feature 1: ValidatePDF**
-  - ? Step 1.1: Application Layer (MediatR Setup + ValidatePDF Feature) - **NEXT**
+  - ? Step 1.2: API Layer (Endpoint + Exception Middleware) - **NEXT**
 
 ### ? Pending
 
@@ -995,6 +1003,7 @@ DocumentOperator.Tests/
 | 17.01.2025 | Tests | DevExpressPdfProcessorTests.cs erstellt (6 Tests) |
 | 17.01.2025 | **ROADMAP** | ?? **Komplett umstrukturiert** (Feature-Driven Development!) |
 | 17.01.2025 | **PHASENPLAN** | ?? **Komplett umstrukturiert** (Feature-basiert + Datum korrigiert) |
+| 17.01.2025 | **Feature 1 - Step 1.1** | ? **ABGESCHLOSSEN** - Application Layer (MediatR, Behaviors, ValidatePDF Feature, DTOs, Tests) |
 
 ---
 

DocumentOperator.Application/Common/Behaviors/LoggingBehavior.cs

@@ -0,0 +1,66 @@
+using MediatR;
+using Microsoft.Extensions.Logging;
+using System.Diagnostics;
+
+namespace DocumentOperator.Application.Common.Behaviors;
+
+/// <summary>
+/// MediatR Pipeline Behavior that logs requests and tracks performance
+/// Executes AFTER ValidationBehavior, BEFORE Handler
+/// </summary>
+public class LoggingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : IRequest<TResponse>
+{
+    private readonly ILogger<LoggingBehavior<TRequest, TResponse>> _logger;
+
+    public LoggingBehavior(ILogger<LoggingBehavior<TRequest, TResponse>> logger)
+    {
+        _logger = logger;
+    }
+
+    public async Task<TResponse> Handle(
+        TRequest request,
+        RequestHandlerDelegate<TResponse> next,
+        CancellationToken cancellationToken)
+    {
+        var requestName = typeof(TRequest).Name;
+
+        // Request Start
+        _logger.LogInformation("Handling {RequestName}: {@Request}", requestName, request);
+
+        // Performance Tracking
+        var stopwatch = Stopwatch.StartNew();
+
+        try
+        {
+            // Handler ausführen
+            var response = await next();
+
+            stopwatch.Stop();
+
+            // Request Success
+            _logger.LogInformation(
+                "Handled {RequestName} in {ElapsedMs}ms",
+                requestName,
+                stopwatch.ElapsedMilliseconds
+            );
+
+            return response;
+        }
+        catch (Exception ex)
+        {
+            stopwatch.Stop();
+
+            // Request Failed
+            _logger.LogError(
+                ex,
+                "Error handling {RequestName} after {ElapsedMs}ms: {ErrorMessage}",
+                requestName,
+                stopwatch.ElapsedMilliseconds,
+                ex.Message
+            );
+
+            throw; // Exception weiterwerfen (wird von Exception Middleware gefangen)
+        }
+    }
+}

DocumentOperator.Application/Common/Behaviors/ValidationBehavior.cs

@@ -0,0 +1,54 @@
+using FluentValidation;
+using MediatR;
+
+namespace DocumentOperator.Application.Common.Behaviors;
+
+/// <summary>
+/// MediatR Pipeline Behavior that validates requests using FluentValidation
+/// Executes BEFORE the Handler
+/// </summary>
+public class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : IRequest<TResponse>
+{
+    private readonly IEnumerable<IValidator<TRequest>> _validators;
+
+    public ValidationBehavior(IEnumerable<IValidator<TRequest>> validators)
+    {
+        _validators = validators;
+    }
+
+    public async Task<TResponse> Handle(
+        TRequest request,
+        RequestHandlerDelegate<TResponse> next,
+        CancellationToken cancellationToken)
+    {
+        // Wenn keine Validators registriert sind, direkt weiter zum Handler
+        if (!_validators.Any())
+        {
+            return await next();
+        }
+
+        // Validation Context erstellen
+        var context = new ValidationContext<TRequest>(request);
+
+        // Alle Validators parallel ausführen
+        var validationResults = await Task.WhenAll(
+            _validators.Select(v => v.ValidateAsync(context, cancellationToken))
+        );
+
+        // Fehler sammeln
+        var failures = validationResults
+            .Where(r => !r.IsValid)
+            .SelectMany(r => r.Errors)
+            .ToList();
+
+        // Bei Fehlern: ValidationException werfen (wird von Exception Middleware gefangen)
+        if (failures.Any())
+        {
+            throw new ValidationException(failures);
+        }
+
+        // Validation erfolgreich ? weiter zum Handler
+        return await next();
+    }
+}

DocumentOperator.Application/Common/DTOs/ValidatePdfRequest.cs

@@ -0,0 +1,7 @@
+namespace DocumentOperator.Application.Common.DTOs;
+
+/// <summary>
+/// Request DTO for ValidatePdf endpoint
+/// </summary>
+/// <param name="Base64Pdf">PDF content as Base64 string</param>
+public record ValidatePdfRequest(string Base64Pdf);

DocumentOperator.Application/Common/DTOs/ValidatePdfResponse.cs

@@ -0,0 +1,14 @@
+namespace DocumentOperator.Application.Common.DTOs;
+
+/// <summary>
+/// Response DTO for ValidatePdf endpoint
+/// Contains PDF metadata
+/// </summary>
+public record ValidatePdfResponse(
+    int PageCount,
+    long FileSizeBytes,
+    double FileSizeMB,
+    string PdfVersion,
+    bool HasAttachments,
+    int AttachmentCount
+);

DocumentOperator.Application/DependencyInjection.cs

@@ -0,0 +1,33 @@
+using FluentValidation;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DocumentOperator.Application;
+
+/// <summary>
+/// Dependency Injection configuration for Application Layer
+/// </summary>
+public static class DependencyInjection
+{
+    /// <summary>
+    /// Registers Application Layer services (MediatR, FluentValidation, Behaviors)
+    /// </summary>
+    public static IServiceCollection AddApplication(this IServiceCollection services)
+    {
+        var assembly = typeof(DependencyInjection).Assembly;
+
+        // Register MediatR (scannt Assembly nach Handlers)
+        services.AddMediatR(config =>
+        {
+            config.RegisterServicesFromAssembly(assembly);
+
+            // Pipeline Behaviors (Reihenfolge wichtig!)
+            config.AddOpenBehavior(typeof(Common.Behaviors.ValidationBehavior<,>));
+            config.AddOpenBehavior(typeof(Common.Behaviors.LoggingBehavior<,>));
+        });
+
+        // Register FluentValidation (scannt Assembly nach Validators)
+        services.AddValidatorsFromAssembly(assembly);
+
+        return services;
+    }
+}

DocumentOperator.Application/DocumentOperator.Application.csproj

@@ -17,15 +17,12 @@
   </ItemGroup>
 
   <ItemGroup>
-    <Folder Include="Common\Behaviors\" />
-    <Folder Include="Common\DTOs\" />
     <Folder Include="Common\Mappings\" />
     <Folder Include="DependencyInjection\" />
     <Folder Include="Features\Documents\ExtractAttachments\" />
     <Folder Include="Features\Documents\ConcatenatePdfs\" />
     <Folder Include="Features\Documents\ApplyStamp\" />
     <Folder Include="Features\Documents\EmbedCertificate\" />
-    <Folder Include="Features\Documents\ValidatePdf\" />
   </ItemGroup>
 
 </Project>

DocumentOperator.Application/Features/Documents/ValidatePdf/ValidatePdfHandler.cs

@@ -0,0 +1,33 @@
+using DocumentOperator.Application.Common.Interfaces;
+using DocumentOperator.Domain.Models.ValueObjects;
+using MediatR;
+
+namespace DocumentOperator.Application.Features.Documents.ValidatePdf;
+
+/// <summary>
+/// Handler for ValidatePdfQuery
+/// Orchestrates PDF validation using IPdfProcessor
+/// </summary>
+public class ValidatePdfHandler : IRequestHandler<ValidatePdfQuery, PdfMetadata>
+{
+    private readonly IPdfProcessor _pdfProcessor;
+
+    public ValidatePdfHandler(IPdfProcessor pdfProcessor)
+    {
+        _pdfProcessor = pdfProcessor;
+    }
+
+    /// <summary>
+    /// Validates PDF and returns metadata
+    /// </summary>
+    public async Task<PdfMetadata> Handle(ValidatePdfQuery request, CancellationToken cancellationToken)
+    {
+        // Value Object ? Byte Array
+        byte[] pdfBytes = request.PdfContent.ToByteArray();
+
+        // DevExpress Service aufrufen (kann PdfProcessingException werfen)
+        var metadata = await _pdfProcessor.ValidateAsync(pdfBytes);
+
+        return metadata;
+    }
+}

DocumentOperator.Application/Features/Documents/ValidatePdf/ValidatePdfQuery.cs

@@ -0,0 +1,10 @@
+using DocumentOperator.Domain.Models.ValueObjects;
+using MediatR;
+
+namespace DocumentOperator.Application.Features.Documents.ValidatePdf;
+
+/// <summary>
+/// Query to validate a PDF document and return metadata
+/// </summary>
+/// <param name="PdfContent">PDF content as Base64 string (validated by Value Object)</param>
+public record ValidatePdfQuery(Base64String PdfContent) : IRequest<PdfMetadata>;

DocumentOperator.Application/Features/Documents/ValidatePdf/ValidatePdfValidator.cs

@@ -0,0 +1,17 @@
+using FluentValidation;
+
+namespace DocumentOperator.Application.Features.Documents.ValidatePdf;
+
+/// <summary>
+/// Validator for ValidatePdfQuery
+/// Validates that PdfContent is not null (Base64String already validates format in its constructor)
+/// </summary>
+public class ValidatePdfValidator : AbstractValidator<ValidatePdfQuery>
+{
+    public ValidatePdfValidator()
+    {
+        RuleFor(x => x.PdfContent)
+            .NotNull()
+            .WithMessage("PDF content is required");
+    }
+}

DocumentOperator.Tests/Unit/Application/Features/ValidatePdf/ValidatePdfHandlerTests.cs

@@ -0,0 +1,78 @@
+using DocumentOperator.Application.Common.Interfaces;
+using DocumentOperator.Application.Features.Documents.ValidatePdf;
+using DocumentOperator.Domain.Common.Exceptions;
+using DocumentOperator.Domain.Models.ValueObjects;
+using FluentAssertions;
+using Moq;
+using Xunit;
+
+namespace DocumentOperator.Tests.Unit.Application.Features.ValidatePdf;
+
+public class ValidatePdfHandlerTests
+{
+    private readonly Mock<IPdfProcessor> _mockPdfProcessor;
+    private readonly ValidatePdfHandler _handler;
+
+    public ValidatePdfHandlerTests()
+    {
+        _mockPdfProcessor = new Mock<IPdfProcessor>();
+        _handler = new ValidatePdfHandler(_mockPdfProcessor.Object);
+    }
+
+    [Fact]
+    public async Task Handle_ValidPdf_ReturnsPdfMetadata()
+    {
+        // Arrange
+        var base64Pdf = Convert.ToBase64String(new byte[] { 0x25, 0x50, 0x44, 0x46 }); // "%PDF"
+        var pdfContent = Base64String.Create(base64Pdf);
+        var query = new ValidatePdfQuery(pdfContent);
+
+        var expectedMetadata = new PdfMetadata(
+            pageCount: 5,
+            fileSizeBytes: 1024,
+            pdfVersion: "1.4",
+            hasAttachments: false,
+            attachmentCount: 0
+        );
+
+        _mockPdfProcessor
+            .Setup(x => x.ValidateAsync(It.IsAny<byte[]>()))
+            .ReturnsAsync(expectedMetadata);
+
+        // Act
+        var result = await _handler.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.PageCount.Should().Be(5);
+        result.FileSizeBytes.Should().Be(1024);
+        result.PdfVersion.Should().Be("1.4");
+        result.HasAttachments.Should().BeFalse();
+        result.AttachmentCount.Should().Be(0);
+
+        _mockPdfProcessor.Verify(
+            x => x.ValidateAsync(It.IsAny<byte[]>()),
+            Times.Once
+        );
+    }
+
+    [Fact]
+    public async Task Handle_PdfProcessorThrowsException_PropagatesException()
+    {
+        // Arrange
+        var base64Pdf = Convert.ToBase64String(new byte[] { 0x25, 0x50, 0x44, 0x46 });
+        var pdfContent = Base64String.Create(base64Pdf);
+        var query = new ValidatePdfQuery(pdfContent);
+
+        _mockPdfProcessor
+            .Setup(x => x.ValidateAsync(It.IsAny<byte[]>()))
+            .ThrowsAsync(new PdfProcessingException("Invalid PDF format"));
+
+        // Act
+        Func<Task> act = async () => await _handler.Handle(query, CancellationToken.None);
+
+        // Assert
+        await act.Should().ThrowAsync<PdfProcessingException>()
+            .WithMessage("Invalid PDF format");
+    }
+}