[jira] [Created] (PDFBOX-5528) PDF/UA: Add marked content sections when flattening acro forms

["Andre (Jira)" <ji...@apache.org>]

Andre created PDFBOX-5528:
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             Summary: PDF/UA: Add marked content sections when flattening acro forms
                 Key: PDFBOX-5528
                 URL: https://issues.apache.org/jira/browse/PDFBOX-5528
             Project: PDFBox
          Issue Type: Improvement
          Components: AcroForm
            Reporter: Andre
         Attachments: correct.png, wrong.png

We need to support PDF/UA compliant documents to some extent. I noticed that when we take a PDF/UA compliant PDF document and flatten it via PDAcroForm#flatten, the resulting output is not PDF/UA compliant anymore.

After a little bit of research, the problem is that PDFBox creates /DO operators with paths representing the appearance of the form fields. According to the PDF/UA standard, such paths need to be enclosed in marked content sections (BMC ... EMC, BDC ... EMC, see attached images)

By copying some code from AcroForm#flatten and adding contentStream.beginMarkedContent and contentStream.endMarkedContent myself, I can workaround the problem, but that's less than ideal, it would be great if this could be included in PDFBox.

<pre> 

           final var dict = new COSDictionary();
           dict.setLong(COSName.MCID, mcid);
           dict.setItem(COSName.BBOX, bBox);
           dict.setItem(COSName.TYPE, COSName.BACKGROUND);
            final var propList = PDPropertyList.create(dict);
            contentStream.beginMarkedContent(COSName.ARTIFACT, propList);

            contentStream.saveGraphicsState();

            // see https://stackoverflow.com/a/54091766/1729265 for an explanation
            // of the steps required
            // this will transform the appearance stream form object into the rectangle of the
            // annotation bbox and map the coordinate systems
            final var transformationMatrix = pdfbox_resolveTransformationMatrix(form, annotation, appearanceStream);

            contentStream.transform(transformationMatrix);
            contentStream.drawForm(fieldObject);
            contentStream.restoreGraphicsState();

            contentStream.endMarkedContent();

</pre>



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