diff --git a/DocumentOperator.API/ROADMAP.md b/DocumentOperator.API/ROADMAP.md
index 400d3e8..847476e 100644
--- a/DocumentOperator.API/ROADMAP.md
+++ b/DocumentOperator.API/ROADMAP.md
@@ -1321,11 +1321,12 @@ public async Task POST_ValidatePdf_InvalidPdf_Returns400() { }
     - ? Step 3.2.1 - ProcessDocument Ordner gelöscht (Application Layer cleanup)
     - ? Step 3.2.2 - Test-Ordnerstruktur erstellt (Unit/Infrastructure/Services/PdfProcessing)
     - ? Step 3.2.3 - Test-PDF Datei hinzugefügt (valid.pdf als Embedded Resource)
+    - ? Step 3.2.4 - DevExpressPdfProcessorTests.cs erstellt (TDD Red Phase - 6 Tests)
 
 ### ?? In Progress
 - **Phase 3, Step 3.2:** DevExpressPdfProcessor (TDD)
-  - **NEXT:** Step 3.2.4 - DevExpressPdfProcessorTests.cs erstellen (TDD Red Phase)
-  - **Progress:** 3/7 Mini-Steps abgeschlossen
+  - **NEXT:** Step 3.2.5 - DevExpressPdfProcessor.cs implementieren (TDD Green Phase)
+  - **Progress:** 4/7 Mini-Steps abgeschlossen
 
 ### ? Pending
 - **Phase 3:** Infrastructure Layer
@@ -1484,6 +1485,7 @@ public async Task POST_ValidatePdf_InvalidPdf_Returns400() { }
 | 17.01.2025 | Application | ? Step 3.2.1 - ProcessDocument Ordner gelöscht (Cleanup) |
 | 17.01.2025 | Tests | ? Step 3.2.2 - Test-Ordnerstruktur erstellt, UnitTest1.cs gelöscht |
 | 17.01.2025 | Tests | ? Step 3.2.3 - Test-PDF (valid.pdf) als Embedded Resource hinzugefügt |
+| 17.01.2025 | Tests | ? Step 3.2.4 - DevExpressPdfProcessorTests.cs erstellt (TDD Red - 6 Tests) |
 
 ---
 
diff --git a/DocumentOperator.Tests/DocumentOperator.Tests.csproj b/DocumentOperator.Tests/DocumentOperator.Tests.csproj
index 5a024dd..41ec07f 100644
--- a/DocumentOperator.Tests/DocumentOperator.Tests.csproj
+++ b/DocumentOperator.Tests/DocumentOperator.Tests.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>net8.0</TargetFramework>
@@ -39,8 +39,4 @@
     <ProjectReference Include="..\DocumentOperator.Infrastructure\DocumentOperator.Infrastructure.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Folder Include="Unit\Infrastructure\Services\PdfProcessing\" />
-  </ItemGroup>
-
 </Project>
diff --git a/DocumentOperator.Tests/Unit/Infrastructure/Services/PdfProcessing/DevExpressPdfProcessorTests.cs b/DocumentOperator.Tests/Unit/Infrastructure/Services/PdfProcessing/DevExpressPdfProcessorTests.cs
new file mode 100644
index 0000000..c74046a
--- /dev/null
+++ b/DocumentOperator.Tests/Unit/Infrastructure/Services/PdfProcessing/DevExpressPdfProcessorTests.cs
@@ -0,0 +1,146 @@
+using System.Reflection;
+using DocumentOperator.Application.Common.Interfaces;
+using DocumentOperator.Domain.Common.Exceptions;
+using DocumentOperator.Domain.Models.ValueObjects;
+using DocumentOperator.Infrastructure.Services.PdfProcessing;
+using FluentAssertions;
+
+namespace DocumentOperator.Tests.Unit.Infrastructure.Services.PdfProcessing;
+
+/// <summary>
+/// Unit tests for DevExpressPdfProcessor.
+/// Tests PDF validation and metadata extraction.
+/// </summary>
+public class DevExpressPdfProcessorTests
+{
+    private readonly IPdfProcessor _sut; // SUT = System Under Test
+
+    public DevExpressPdfProcessorTests()
+    {
+        // Arrange: Create instance (wird später implementiert)
+        _sut = new DevExpressPdfProcessor();
+    }
+
+    #region Helper Methods
+
+    /// <summary>
+    /// Loads a test PDF from embedded resources.
+    /// </summary>
+    /// <param name="filename">Name of the PDF file (e.g., "valid.pdf")</param>
+    /// <returns>PDF content as byte array</returns>
+    private static byte[] LoadTestPdf(string filename)
+    {
+        var assembly = Assembly.GetExecutingAssembly();
+        var resourceName = $"DocumentOperator.Tests.TestData.Pdfs.{filename}";
+
+        using var stream = assembly.GetManifestResourceStream(resourceName);
+
+        if (stream == null)
+        {
+            throw new FileNotFoundException(
+                $"Embedded resource '{resourceName}' not found. " +
+                $"Available resources: {string.Join(", ", assembly.GetManifestResourceNames())}");
+        }
+
+        using var memoryStream = new MemoryStream();
+        stream.CopyTo(memoryStream);
+        return memoryStream.ToArray();
+    }
+
+    #endregion
+
+    #region ValidateAsync Tests
+
+    [Fact]
+    public async Task ValidateAsync_ValidPdf_ReturnsPdfMetadata()
+    {
+        // Arrange
+        byte[] pdfBytes = LoadTestPdf("valid.pdf");
+
+        // Act
+        var metadata = await _sut.ValidateAsync(pdfBytes);
+
+        // Assert
+        metadata.Should().NotBeNull("a valid PDF should return metadata");
+        metadata.PageCount.Should().BeGreaterThan(0, "PDF must have at least one page");
+        metadata.FileSizeBytes.Should().Be(pdfBytes.Length, "file size should match input");
+        metadata.PdfVersion.Should().NotBeNullOrEmpty("PDF version should be detected");
+    }
+
+    [Fact]
+    public async Task ValidateAsync_ValidPdf_ReturnsCorrectPageCount()
+    {
+        // Arrange
+        byte[] pdfBytes = LoadTestPdf("valid.pdf");
+
+        // Act
+        var metadata = await _sut.ValidateAsync(pdfBytes);
+
+        // Assert
+        // Deine valid.pdf hat wahrscheinlich 1-5 Seiten - passe an!
+        metadata.PageCount.Should().BeInRange(1, 100, "test PDF should have reasonable page count");
+    }
+
+    [Fact]
+    public async Task ValidateAsync_NullBytes_ThrowsPdfProcessingException()
+    {
+        // Arrange
+        byte[]? pdfBytes = null;
+
+        // Act
+        Func<Task> act = async () => await _sut.ValidateAsync(pdfBytes!);
+
+        // Assert
+        await act.Should().ThrowAsync<PdfProcessingException>()
+            .WithMessage("*null*", "null input should be rejected");
+    }
+
+    [Fact]
+    public async Task ValidateAsync_EmptyBytes_ThrowsPdfProcessingException()
+    {
+        // Arrange
+        byte[] pdfBytes = Array.Empty<byte>();
+
+        // Act
+        Func<Task> act = async () => await _sut.ValidateAsync(pdfBytes);
+
+        // Assert
+        await act.Should().ThrowAsync<PdfProcessingException>()
+            .WithMessage("*empty*", "empty input should be rejected");
+    }
+
+    [Fact]
+    public async Task ValidateAsync_CorruptedPdf_ThrowsPdfProcessingException()
+    {
+        // Arrange
+        byte[] pdfBytes = "This is not a valid PDF content"u8.ToArray();
+
+        // Act
+        Func<Task> act = async () => await _sut.ValidateAsync(pdfBytes);
+
+        // Assert
+        await act.Should().ThrowAsync<PdfProcessingException>()
+            .WithMessage("*invalid*", "corrupted PDF should throw exception");
+    }
+
+    #endregion
+
+    #region Metadata Tests
+
+    [Fact]
+    public async Task ValidateAsync_ValidPdf_FileSizeMBCalculatedCorrectly()
+    {
+        // Arrange
+        byte[] pdfBytes = LoadTestPdf("valid.pdf");
+
+        // Act
+        var metadata = await _sut.ValidateAsync(pdfBytes);
+
+        // Assert
+        double expectedSizeMB = pdfBytes.Length / 1024.0 / 1024.0;
+        metadata.FileSizeMB.Should().BeApproximately(expectedSizeMB, 0.01,
+            "FileSizeMB should be calculated correctly from bytes");
+    }
+
+    #endregion
+}
\ No newline at end of file