Unable to Verify Signature after 250 Pages

[⠀MG⠀]

I have Can anyone help in this is problem ? I have a pdf of 312 pages and all pages are digitally signed from a digital signature pendrive which is issued by a trusted authority, Problem is i am unable to verify signature after 250 pages means from page 1-250 all pages shows signature is valid, from 251-311 it says unable to verify signatures it shows me red cross and at last page 312 it again shows that signature is verified.If it was problem of pdf then please note that i have already tried it with many pdfs there is not a problem from pdf side, i think only adobe reader cannot verify siganture after 250 pages. Please someone help me in this.

[try67]

There is absolutely no need to sign every page in the file. A digital signature applies to the entire file as a whole, not just to the page where it is placed. In fact, it doesn't need to appear on any page at all, and can still be valid.

Signing a file so many times is very likely to destabilize it. Inform whoever did this that it's not necessary at all.

[⠀MG⠀]

I understand your concern that a single signature is valid for whole doument but when it comes to digital sign a legal document where a person is required to sign every page where it is mentioned that at this area in this pdf on this page no signature is required then we have to do, i need a explanation why i am unable to validate signature after 250 pages. Please help.

[try67]

This is not a logical requirement, but OK. If you really need a "visual" signature on each page use something like a stamp and then digitally sign the file once at the end.

As I said, that many (digital) signatures can destabilize a file and even corrupt it. I'm guessing this is what happened here.

[⠀MG⠀]

Alright, But the thing which i didnt share was that all signature are getting visually verified in "PDF X" & "FOXIT PDF READER" thats what my main concern is i cant say everyone to use these software as majority of people used adobe to verify digitally signed pdf so it hard for me to explain every one to use these particular software to verify digitally signed pdf on more than 250 pages as per my personal opinion too adobe reader is easy and comfortable to use that why i want solution in adobe only, else i can use other software too but difficult to tell my thousands of customer to use other software just to verify digital signature, also i have attached dummy signed pdf for your reference which you can test on both software.

[⠀MG⠀]

As per our mail conversation no supported received yet, As you suggested on mail free version of Adobe cannot fullfill my request, I have installed Adobe Acrobat 2020 Pro trial for 7 days but it is also showing Invalid signature after 250 pages, is there any problem with Adobe only that it cannot verify signature after 250 pages ??

[MikelKlink]

I tested again with your example file. To me it now looks like there is a limit to the number of concurrently opened documents in Acrobat and that each validated signature keeps one or more documents open.

I opened your document with validation-on-startup turned off and then manually validated 247 of the signatures. Then I started opening additional files in that Acrobat session, and fairly quickly (with two or three additional PDFs) I got to see either

or

So I assume each validated entry on the signature panel opens and keeps open one (probably the signed revision) or more (possibly following revisions) revisions of the PDF under scrutiny as independent PDF documents, and as soon as the internal document table is full, further validations fail.

Unfortunately further validations don't fail with more appropriate error messages like those above but with the claim that "the document has been altered or corrupted since the signature was applied."

Googl'ing around I learn that in the early Acrobat versions there appears to have been a limit of 20 files and later of about 50 files. Now I'd guess the limit has been increased to approximately 256 files which is not enough for validating many signatures.

[⠀MG⠀]

Hey,

Could you please share me what did you found on Google.

[MikelKlink]

Could you please share me what did you found on Google.

Nothing peculiar, acrobat limit open files, and the numbers occurring most often in the results were 20 and 50.

The relation of this limit  to the signatures came up because of the message boxes I got during the experiment.

[⠀MG⠀]

I wanna deeply understand it, I am also technical sounded but what you checked i wanna know that too. It may help me.

[MikelKlink]

I am not sure what you are asking for.

I googled for “acrobat limit open files“ (which you can do, too), and in the articles Google shows in response you can read that early versions of Acrobat could only open 20 files at a time and that later this limit seems to have increased to 50 files. 

Considering the finding in the case at hand one may conjecture that Acrobat now can open some 250 files. But not only explicitly opened files count here but also documents opened under the hood by Acrobat, like signed document revisions or configuration cos files.

[MikelKlink]

As I said, that many (digital) signatures can destabilize a file and even corrupt it.

Well, strictly speaking it's not those many digital signatures that destabilize or corrupt the PDF file, but it's the software that cannot handle such a file. According to the spec no limit is mentioned on the number of digital signatures (or incremental updates) in a PDF. And 250 is not an unreasonably large number either.

Nonetheless the use case of the op indeed is questionable, and if some legal system indeed requires digitally signed documents to have a digital signature visualization on each document page, this legal system is not fit for the digital age.

[MikelKlink]

If you configure Acrobat to not validate the signatures on startup (Preferences -> Signatures -> Verification -> Verify signatures when document is opened), Acrobat opens your file without issue. And if you then choose some individual signatures on the Signature Panel and click "Validate Signature" in their respective context menus, you'll see that you can successfully validate all of them.

Thus, Acrobat can verify siganture after 250 pages, you merely have to do it manually and probably close and re-open the file each time after verifying some 50 signatures.

Alternatively you can try some other signature validators. Beware, though, validation web services are likely to run into timeouts when validating all the signatures of your document.

[⠀MG⠀]

It is set to automatically validate after opening because when even i open PDF It starts a long process to verify each signature then when all signature gets verfied from CRL Url or certifiying authority, then pdf gets loaded with signed pages and as usual currently facing issue of red cross after 250 signatures.

[MikelKlink]

With default settings the current Acrobat version apparently cannot properly validate files with many digital signatures like yours.

My previous answer only pointed out that Acrobat can validate all the signatures in your document by manual work and re-opening the PDF multiple times. But this of course is nothing you can expect others to do who have to validate the signatures in your document as part of their job.

[Raeben]

If as as stated below the limiting factor is the number of pages perhaps changing the page size would remedy.

[MikelKlink]

If as as stated below the limiting factor is the number of pages perhaps changing the page size would remedy.

The number of pages is limiting only because the op wants to "digitally sign each page". The actual limiting factor is the number of digital signatures.

Also for the legal documents mentioned by the op there may be a prescribed page size for such communications.

[shaktikeshri]

Hi,

Sorry for the inconvenience caused. We are able to reproduce the issue in the testfile shared by you. We are investigating further to debug the issue here. Is there any specific reason that signing is required on each page?

Thanks,

Shakti K

[⠀MG⠀]

Is there any specific reason that signing is required on each page?

Hi,

Yes all the document in PDF are necessary to sign on each page, due to some legal reason, In short every page comes with a different agreement so it is mendatory to sign on every page.

Thanks & Regards

Mayank Gupta

[MikelKlink]

If the pages constitute different legal agreements, have you considered putting them in separate single-page documents, signing each of them, and bundling them in a portable collection (aka portfolio)?

[⠀MG⠀]

If the pages constitute different legal agreements, have you considered putting them in separate single-page documents, signing each of them, and bundling them in a portable collection (aka portfolio)?

Hi it would be difficult for us maintaining n numbers of single file as this is just one file which i have shared for demo and we have lakhs of pages which are generated everyday, i know that solution too, but if i have raised a query it means i have tried all of my best, i am also technical sounded but in this situation only adobe could help,, In a single PDF we have approx 1000 pages so its easy to maintain 100 PDF instead of single single lakhs of PDF everyday.

[MikelKlink]

The portable collection / portfolio I mentioned would also be a single PDF file, and merely for signing the single pages would exist as individual stand-alone documents.

I have to admit, though, that the appearance and presentation of the posrtable collection document would be different from the current ducoment. I don't know whether it would be in line with your requirements.

It may be worth a try, though.

[S. S]

Hi @⠀MG⠀,

Hope you are doing well. 

We have logged a ticket to work further on this.

I will keep the thread updated as we make progress.

We request your kind understanding and patience while the team investigates further.

Thanks,
Souvik

[⠀MG⠀]

Hi Souvik,

I’m doing well, thank you! Hope you’re doing well too.

Thank you for the update. I appreciate your efforts in addressing this issue & will be waiting for a solution as soon as possible.

Looking forward to hearing from you soon.

Thanks & Regards

Mayank Gupta

[S. S]

@⠀MG⠀,

Happy to help!

-Souvik