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https://issues.apache.org/jira/browse/TIKA-4756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18088299#comment-18088299
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Tim Allison commented on TIKA-4756:
-----------------------------------
What I can't figure out without the file is why Tika didn't label that as "has
signature" if the file actually had a signature.
The PR that I opened will now flag a PDF even if all signatures are empty with
a "has signature field" item. However, Tika _should_ have tagged the
screenshotted pdf with "has signature" already.
[~willytk] I can't imagine you can share the original file with me?
[~tilman] any idea why Tika's code wasn't finding a signature?
> Detecting Signatures in PDFs with AcroForm
> ------------------------------------------
>
> Key: TIKA-4756
> URL: https://issues.apache.org/jira/browse/TIKA-4756
> Project: Tika
> Issue Type: Improvement
> Components: metadata
> Reporter: Willy T. Koch
> Priority: Minor
> Labels: Signature
> Attachments: sigflags_sample.pdf, signature.png
>
>
> We see that PDFs that have an Acroform that contains a signture /Sig fields
> aren't detected by the /meta analysis. It detects the AcroForm with
> "pdf:hasAcroFormFields": "true", but nothing on the /Sig part. They are
> created directly in Adobe Acrobat which is also possible in the Free version.
> It would be very useful to also return "hasSignature": "true" (or some
> other signature: property) in these kinds of filees, so we can handle it on
> our end. We use this to exluce PDFs with digital signatures from being
> reconverted to PDF/A.
>
> When I run it through the OCRmyPDF, it flags it as digitally signed and
> exits, which is how I first noticed it.
> _ocrmypdf sigflags_sample.pdf sigflags_sample_ocrmypdf.pdf_
> _DigitalSignatureError: Input PDF has a digital signature. OCR would alter
> the document,_
> _invalidating the signature._
>
> I've attached a small sample PDF with AcroForm and Signature to reproduce the
> issue.
>
> Willy T. Koch
> Technical Product manager,
> Public 360°
> Norway
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