feat: Add PDF/A validation endpoint (Feature 3)

Domain layer:

  - PdfAMetadata value object (isValid, pdfVersion, pageCount, encrypted, pdfaVersion, pdfaCompliant, errors, warnings)

Infrastructure layer:

  - IPdfProcessor.ValidatePdfAAsync() interface method

  - DevExpressPdfProcessor.ValidatePdfAAsync() implementation

  - DetectEncryption() - scans PDF raw data for /Encrypt keyword

  - DetectPdfAConformance() - parses XMP metadata (pdfaid:part, pdfaid:conformance)

  - Validation: encrypted PDF cannot be PDF/A compliant

Application layer:

  - ValidatePdfAQuery + ValidatePdfAQueryHandler (co-located)

  - ValidatePdfAQueryValidator (FluentValidation: PdfBytes XOR Base64Pdf)

  - PdfAValidationResult DTO

  - AutoMapper: PdfAMetadata -> PdfAValidationResult

API layer:

  - PdfValidationController.ValidatePdfAFromFile() (multipart/form-data)

  - PdfValidationController.ValidatePdfAFromBase64() (application/json)

  - XML documentation with response codes

Result:

  - POST /api/pdf/validation/validate-pdfa (both multipart and JSON)

  - Returns: conformance level, errors, warnings

  - Build: 0 errors, 4 warnings (DevExpress eval)

  - Tests: 20/20 passing

Next: Integration tests + Swagger test case

DocumentOperator.API/Controllers/PdfValidationController.cs

@@ -1,5 +1,6 @@
 using DocumentOperator.Application.Common.DTOs;
 using DocumentOperator.Application.ValidatePdf.Queries;
+using DocumentOperator.Application.ValidatePdfA.Queries;
 using MediatR;
 using Microsoft.AspNetCore.Mvc;
 
@@ -76,4 +77,68 @@ public class PdfValidationController(IMediator Mediator) : ControllerBase
         
         return Ok(result);
     }
+
+    /// <summary>
+    /// Validates a PDF/A document and checks conformance level (multipart/form-data)
+    /// </summary>
+    /// <param name="file">PDF file to validate</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>PDF/A metadata (conformance level, errors, warnings)</returns>
+    /// <response code="200">PDF/A validation completed, results returned</response>
+    /// <response code="400">Invalid PDF or file format</response>
+    /// <response code="500">Internal server error during validation</response>
+    [HttpPost("validate-pdfa")]
+    [Consumes("multipart/form-data")]
+    [ProducesResponseType(typeof(PdfAValidationResult), StatusCodes.Status200OK)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status500InternalServerError)]
+    public async Task<IActionResult> ValidatePdfAFromFile(
+        IFormFile file,
+        CancellationToken cancellationToken)
+    {
+        if (file == null || file.Length == 0)
+        {
+            return BadRequest(new ProblemDetails
+            {
+                Title = "Invalid file",
+                Detail = "File is required and cannot be empty",
+                Status = StatusCodes.Status400BadRequest
+            });
+        }
+
+        // Convert IFormFile to byte array
+        using var memoryStream = new MemoryStream();
+        await file.CopyToAsync(memoryStream, cancellationToken);
+        byte[] pdfBytes = memoryStream.ToArray();
+
+        // Direct pass-through to MediatR
+        var query = new ValidatePdfAQuery { PdfBytes = pdfBytes };
+        var result = await Mediator.Send(query, cancellationToken);
+        
+        return Ok(result);
+    }
+
+    /// <summary>
+    /// Validates a PDF/A document and checks conformance level (Base64 JSON)
+    /// </summary>
+    /// <param name="query">PDF as Base64 string</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>PDF/A metadata (conformance level, errors, warnings)</returns>
+    /// <response code="200">PDF/A validation completed, results returned</response>
+    /// <response code="400">Invalid PDF or Base64 format</response>
+    /// <response code="500">Internal server error during validation</response>
+    [HttpPost("validate-pdfa")]
+    [Consumes("application/json")]
+    [ProducesResponseType(typeof(PdfAValidationResult), StatusCodes.Status200OK)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status500InternalServerError)]
+    public async Task<IActionResult> ValidatePdfAFromBase64(
+        [FromBody] ValidatePdfAQuery query,
+        CancellationToken cancellationToken)
+    {
+        // Direct pass-through to MediatR
+        var result = await Mediator.Send(query, cancellationToken);
+        
+        return Ok(result);
+    }
 }