feat:(pdfa-conversion) Implement Strict PDF/A Mode with Verification (#5663)

# Description of Changes


This PR introduces a new "Strict Mode" for the PDF to PDF/A conversion
tool. When enabled, the application will use VeraPDF to verify that the
resulting file is perfectly compliant with the selected PDF/A standard.
If validation fails, the system will return a descriptive error instead
of a non-compliant file.



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---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Signed-off-by: Balázs Szücs <bszucs1209@gmail.com>

app/core/src/main/java/stirling/software/SPDF/controller/api/converters/ConvertPDFToPDFA.java

@@ -71,10 +71,12 @@ import org.apache.xmpbox.schema.PDFAIdentificationSchema;
 import org.apache.xmpbox.schema.XMPBasicSchema;
 import org.apache.xmpbox.xml.DomXmpParser;
 import org.apache.xmpbox.xml.XmpSerializer;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.ModelAttribute;
 import org.springframework.web.multipart.MultipartFile;
+import org.springframework.web.server.ResponseStatusException;
 
 import io.github.pixee.security.Filenames;
 import io.swagger.v3.oas.annotations.Operation;
@@ -99,6 +101,7 @@ public class ConvertPDFToPDFA {
 
     private static final Pattern NON_PRINTABLE_ASCII = Pattern.compile("[^\\x20-\\x7E]");
     private final RuntimePathConfig runtimePathConfig;
+    private final stirling.software.SPDF.service.VeraPDFService veraPDFService;
 
     private static final String ICC_RESOURCE_PATH = "/icc/sRGB2014.icc";
     private static final int PDFA_COMPATIBILITY_POLICY = 1;
@@ -587,7 +590,8 @@ public class ConvertPDFToPDFA {
         if (isPdfX) {
             return handlePdfXConversion(inputFile, outputFormat);
         } else {
-            return handlePdfAConversion(inputFile, outputFormat);
+            return handlePdfAConversion(
+                    inputFile, outputFormat, request.getStrict() != null && request.getStrict());
         }
     }
 
@@ -1793,7 +1797,7 @@ public class ConvertPDFToPDFA {
     }
 
     private ResponseEntity<byte[]> handlePdfAConversion(
-            MultipartFile inputFile, String outputFormat) throws Exception {
+            MultipartFile inputFile, String outputFormat, boolean strict) throws Exception {
         PdfaProfile profile = PdfaProfile.fromRequest(outputFormat);
 
         // Get the original filename without extension
@@ -1822,6 +1826,10 @@ public class ConvertPDFToPDFA {
 
                     validateAndWarnPdfA(converted, profile, "Ghostscript");
 
+                    if (strict) {
+                        verifyStrictCompliance(converted);
+                    }
+
                     return WebResponseUtils.bytesToWebResponse(
                             converted, outputFilename, MediaType.APPLICATION_PDF);
                 } catch (IOException | InterruptedException e) {
@@ -1839,14 +1847,42 @@ public class ConvertPDFToPDFA {
             // Validate with PDFBox preflight and warn if issues found
             validateAndWarnPdfA(converted, profile, "PDFBox/LibreOffice");
 
+            if (strict) {
+                verifyStrictCompliance(converted);
+            }
+
             return WebResponseUtils.bytesToWebResponse(
                     converted, outputFilename, MediaType.APPLICATION_PDF);
-
         } finally {
             deleteQuietly(workingDir);
         }
     }
 
+    private void verifyStrictCompliance(byte[] pdfBytes) throws IOException {
+        try (InputStream is = new ByteArrayInputStream(pdfBytes)) {
+            List<stirling.software.SPDF.model.api.security.PDFVerificationResult> results =
+                    veraPDFService.validatePDF(is);
+            boolean isCompliant = results.stream().anyMatch(result -> result.isCompliant());
+            if (!isCompliant) {
+                String details =
+                        results.stream()
+                                .map(r -> r.getStandard() + ": " + r.getComplianceSummary())
+                                .collect(Collectors.joining("; "));
+                throw new ResponseStatusException(
+                        HttpStatus.BAD_REQUEST,
+                        "Strict PDF/A mode enabled: Conversion is not perfectly compliant. Details: "
+                                + details);
+            }
+        } catch (Exception e) {
+            if (e instanceof ResponseStatusException) {
+                throw (ResponseStatusException) e;
+            }
+            log.error("Error during strict PDF/A verification", e);
+            throw new ResponseStatusException(
+                    HttpStatus.INTERNAL_SERVER_ERROR, "Error during strict PDF/A verification");
+        }
+    }
+
     private Path sanitizePdfWithPdfBox(Path inputPdf, boolean addWhiteBackground) {
         try {
             Path sanitizedPath =

app/core/src/main/java/stirling/software/SPDF/model/api/converters/PdfToPdfARequest.java

@@ -16,4 +16,9 @@ public class PdfToPdfARequest extends PDFFile {
             requiredMode = Schema.RequiredMode.REQUIRED,
             allowableValues = {"pdfa", "pdfa-1", "pdfa-2", "pdfa-2b", "pdfa-3", "pdfa-3b", "pdfx"})
     private String outputFormat;
+
+    @Schema(
+            description =
+                    "If true, the conversion will fail if the output is not perfectly compliant")
+    private Boolean strict = false;
 }