Another Disappearing Signature Situation

[Dylan28127227s4wg]

Hi,

I've seen variations of the disappearing digital signature problem on here, but I haven't seen mine.

I have a PDF with a signature form field.  I click the field and sign/save the document.  The signature shows up in the Signature Panel, and the blue "Signed and all signatures are valid." banner appears up top.  When the PDF is closed and re-opened, the signature disappears from the Signature Panel and the signature text disappears. The form field is still there but hidden until it's moused over.

- I'm using Acrobat Standard Version 2022.003.20314 | 64-bit

- I've updated/repaired/reinstalled to no avail.

- This happens for any document with a form field like this

- It's the same issue for coworkers

- I think this started a month or two ago.  I can't say for sure since I found out about it from others opening the PDFs.

- If I open the PDF in Chrome, it does show the text of the signature.

My steps:

1) I have a PDF needing a signature created in AutoCAD.

2) I run another application which adds the signature form field in question along with seals, text, etc.

   - It's possible that something is wrong with the form field at this phase, but the issue doesn't pop up until the end in Acrobat.

3) I open the PDF in Acrobat.

4) I click the signature field which prompts my signature

5) I sign and save the PDF, and everything looks good.

6) I close and reopen the PDF in Acrobat, and then it's not the same.

I attached relevant files to show the issue.

Initial.pdf - Base PDF before anything is added

Initial_withSigField.pdf - After the signature form field is added before I click sign

signed.jpg - What it looks like in Acrobat after I've signed Initial_withSigField.pdf

Final.pdf - After saving and closing with the signature lost.

Thank you so much for the assistance!

[ls_rbls]

Hi,

Well, I don't have Acrobat Standard, but I tested your PDFs with Acrobat Pro DC and encountered the same issue.

I am not sure if you were aware that for the past three years Adobe have been announcing end of support for Type 1 Fonts.

See here:

• https://helpx.adobe.com/fonts/kb/postscript-type-1-fonts-end-of-support.html

I was able to see this clearly when I try to edit your PDF and add another field object. The signature field together with the new object disappeared and didn't save the changes at all.

So, I opened both your original "PDF Final" document and compared the Document Properties against my edited copy, and indeed, the Type 1 Font was not substituted nor embedded ... everything just disappeared (and I also opened the same test file with a web browser and nothing there).

Only the Tahoma True Type Font appeared embedded in my blank test document but no signature field whatsoever (completely gone).

This in particular, may be related to a lost security restriction after the PDF was processed with PdfPig (just guessing in the blind here).

So, this brings me to ask you if the .Net library that PdfPig is using to produce PDFs is up to date to its latest version.

But in particular, see this wiki of PdfPig with emphasis on Document Creation that was posted in GitHub:

"

The PdfDocumentBuilder creates a new document with no pages or content. First, for text content, a font must be registered with the builder. Currently this supports Standard 14 fonts provided by Adobe by default and TrueType format fonts.

To add a Standard 14 font use:

public AddedFont AddStandard14Font(Standard14Font type)

Or for a TrueType font use:

AddedFont AddTrueTypeFont(IReadOnlyL

• https://github.com/UglyToad/PdfPig/wiki/Document-Creation

That said, see this other link at the beginning of the same topic:

• https://uglytoad.github.io/PdfPig/

My main question is if you had PDF that was created in Acrobat first with a digital signature field using the Prepare Form tool; and then you signed the PDF document immediately before PdfPig produced the final PDF document?

If that was the case, I would say to produce the PDF first with PdfPig, and lastly certify the document with a digital signature using the Certificates tool instead.

[Dylan28127227s4wg]

Wow, now that's impressive!  The documents are passed through PdfPig, but PdfPig doesn't touch it after it's signed.  I'll elaborate on that part of the process.

1) I recieve the document in need of signature.  By default, they contain 30 or so fonts.  I used one of those to create the files I uploaded earlier just with the contents removed.

2) I use another tool to add stamps, texts, and the signature fields.

1.  PdfPig determines the location of the form field but doesn't place it.
2. SpirePDF places the form field at whatever location.  If anything I figured it might be a SpirePDF problem, so I'm in contact with their customer service but nothing yet.
3. PdfPig touches it once more to shuffle pages around.

3) .NET processing is complete.  The Initial_withSigField.pdf is what it would look like at the end. I then open the document in Acrobat and click the field to sign.

For some of these I'll skip the clicking the field phase and just add the digital signature directly with the .NET tool, and those ones work fine.  The signatures persist after closing/re-opening.  Also, if I omit the form field and sign via the Certificates tool instead, that also persists after closing/re-opening.  So that'll be the fallback option.

[ls_rbls]

Very interesting.

[Dylan28127227s4wg]

Thank you for your answer.  If it's my other tools and not Acrobat, it's helpful to narrow it down.

[ls_rbls]

You're welcome.

[MikelKlink]

There are a number of errors in your Initial_withSigField.pdf file, in particular:

• The signature field widget annotation of your document page is a direct object in the Annots array of the page object.
  This is wrong, the Annots array shall contain indirect references to all annotations associated with the page (ISO 32000-2 Table 31 — Entries in a page object). 
• Also this widget annotation is merged with its field, so the field object also is only present as direct object in the page Annots. But again each field in a document’s interactive form shall be defined by a field dictionary, which shall be an indirect object (ISO 32000-2 section 12.7.4 Field dictionaries).
• The signature field widget annotation of your document page in its P entry does not point back to your document page object but instead to another page dictionary that is not included in your document Pages tree, i.e. an unused, orphan page.
  Furthermore, this orphan page object in its Annots does not reference the signature field widget annotation of your document page; it actually cannot do so because that annotation is not an independent indirect object but merely a direct object. Instead the orphan page references yet another signature field widget annotation object.
• The signature field is not referenced from the Fields array of the AcroForm dictionary of the document; it actually cannot because the signature field is not an independent indirect object but merely a direct one. But the Fields array is specified to be the array of references to the document’s root fields (those with no ancestors in the field hierarchy) (ISO 32000-2 Table 224 — Entries in the interactive form dictionary).

This results in a number of errors in Final.pdf, too, a garbage-in, garbage-out situation. All one can blame Adobe Acrobat for in this context, is that it attempts to sign this broken structure instead of rejecting it.

[ls_rbls]

Great information Mike!

This is a whole new learning curve for me.

[Dylan28127227s4wg]

Thank you for the detailed reply.  I'll investigate further with this in mind.

[Rosie34715796vu3b]

I was able to resolve this by "printing" the PDF as an Adobe PDF. Then the file would save without removing the signature.

[MikelKlink]

"Printing" a PDF, even "as an Adobe PDF", automatically removes digital signatures. Depending on the field flags, it may leave the signature appearance in the file. But the resulting PDF is not protected by a digital signature anymore.

[Rosie34715796vu3b]

Thanks for sharing, I was not aware. I just needed to save the file to an archive and the signature remained on the PDF with the notations that it was signed digitally. I can understand how that would not be sufficient in other situations.