Petras created PDFBOX-2816:
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Summary: PDFBox makes disallowed changes when signing a signed
document
Key: PDFBOX-2816
URL: https://issues.apache.org/jira/browse/PDFBOX-2816
Project: PDFBox
Issue Type: Bug
Components: Signing
Affects Versions: 1.8.9
Reporter: Petras
It seems PDFBox make disallowed changes when signing a document, containing
visual appearance. Using the signing example
{{org.apache.pdfbox.examples.signature.CreateSignature}} (modified to use BC
1.52) I signed (invisible signature) a document (_acrosigned.pdf_) containing
signature with visual appearance. After signing Adobe Acrobat for the resulted
pdf (_acrosigned_signed.pdf_) shows an error for the first signature: {quote}
1 Page(s) Modified
Signature is invalid:
Document has been altered or corrupted since it was signed.
{quote}
The first revision is intact after signing, but it seems PDFBox made some
disallowed changes to the document. Adobe in its technical white paper [Adobe
Acrobat 9 Digital Signatures, Changes and
Improvements|http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/reader/pdfs/readercomp_digitalsignatures.pdf]
disallows such changes for the signed document:
* Adding form fields other than signature fields
* Changing page content
Unfortunately, I could not identify the changes which caused this error, though
I notice these changes in structure after signing:
# Default resources (/DR) were droped from AcroForm dictionary;
# An array of annotation dictionaries (value of /Annots in page object) became
direct;
And probably there are more...
I thought the first change was fundamental, noticed that
{{PDDocument#addSignature()}} method removes /DR key for invisible signatures,
removed in 1.8.10-SNAPSHOT sources, but unfortunately it didn't help. Didn't
tried to reuse the same array object for /Annots yet.
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