signature with readonly mark field

[david]

Hello,

I have a pdf with a field mark as read only after signing. This pdf are certified. The problem is when i sign this document (with iText) using visible signature field "signature1" this signature are invalid in Adobe Reader.

If I remove mark only the signature are correct. If I remove the certification signature the signature are correct.

Regards,
David


FormulaireRO_diffusé_certifié_rempli.pdf

[mkl]

david,

david wrote

I have a pdf with a field mark as read only after signing. This pdf are certified. The problem is when i sign this document (with iText) using visible signature field "signature1" this signature are invalid in Adobe Reader.

If I remove mark only the signature are correct. If I remove the certification signature the signature are correct.
FormulaireRO_diffusé_certifié_rempli.pdf

This may be due to minute differences between the way iText signs and Adobe software signs --- both being correct by the spec, but the one software thinks the other software did something else than merely signing.

For a more detailled analysis please post the other versions of the PDF, too, i.e. the one signed with iText as is, the one with the read only mark removed, and the one with the read only mark removed and signed with iText.

Regards,   Michael

[david]

FormulaireWithoutRO.pdf
FormulaireWithoutROSignedByIText.pdf
FormulaireWithRO.pdf
FormulaireWithROSignedByAdobe.pdf
FormulaireWithROSignedByIText.pdf

Thank for your response Michael

Here the documents.

[mkl]

David,

david wrote

Here the documents.

I just had the time to inspect your documents.

I was not sure what you meant by "a pdf with a field mark as read only after signing". In your document FormulaireWithRO.pdf I now see that that means that the empty signature field "Signature1" has a /Lock entry of type /SigFieldLock and action /All.

According to the specification (ISO 32000-1:2008) this means that upon signing in that signature field all fields in the document should be locked (Table 233) or shall be locked (Table 232).

Unfortunately I cannot find any explanation there what locking a field means. A priori it could either mean that any PDF tool working with a PDF containing a signed signature field with such an entry should consider all document fields read only, or it could mean that any PDF tool signing an empty signature field containg such a /Lock entry shall explicitly mark all form fields read-only in the process.

Adobe Acrobat and Reader seem to follow the latter interpretation; when signing in Signature1 they mark the field "Texte3" read-only by adding a "/Ff 1" entry; when verifying they expect such a marker.

iText on the other hand does not add a "/Ff 1" mark to that field (or does anything at all along the lines of the latter interpretation). Thus, Adobe Acrobat and Reader consider the signature applied by iText invalid as the form fields in the document don't match their expectations.

I'm not sure whether this lack of clarity in the specification has been fixed somewhere (or I even overlooked some clarification in the document itself) --- and, therefore, iText probably offers only limited support for signing empty signature fields --- or not. The mix of optional ("should") and mandatory ("shall") requirement declaration does not help either.

Essentially you currently should not expect signature fields with lock entries to work in this mixed environment.

Regards,   Michael

[david]

Hello Michael,

According to the specification (ISO 32000-1:2008), I have locked All fields. But my signature are not valide.

Regards, David

FormulaireROSignedWithITextLocked.pdf

[mkl]

David,

david wrote

According to the specification (ISO 32000-1:2008), I have locked All fields. But my signature are not valide.

FormulaireROSignedWithITextLocked.pdf

I'm afraid Adobe Reader X and Acrobat 9 both show some weird behavior here.

1. As a result of checking your signature "Signature1" they claim that the document has been changed and, thus, the signature no longer is valid.

2. On the document tab of the signature properties they both claim that some changes applied to the document after signing were disallowed by the author of the document.

3. BUT when asked to determine the actual list of changes (bottom of the same tab), they both admit that there were no changes to the document at all after signing.

Items 1 and especially 2 do not make any sense as there definitively were no changes after applying your signature.

In essence it seems like you cannot trust Reader or Acrobat to correctly analyze PDFs in this context.

At first glance I spotted the read-only flags (/Ff 1) now added by you. Reverse-engineering what else Acrobat and Reader expect might amount to quite some task...

Regards,   Michael