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Seamountain
Participating Frequently
October 22, 2021
Question

Digital Signature. document changed, invalid signature.

  • October 22, 2021
  • 1 reply
  • 19821 views

Hi, I have a problem when I digitally sign a document in Reader.

Reader states that "the document has changed after signing" but no changes have been made.

I use Reader DC 2021 007 20091 and Windows 10 20H2.

 

Why does Reader say so and state that the signature is invalid?

    1 reply

    Amal.
    Amal.
    Legend
    October 22, 2021

    Hi there

     

    Hope you are doing well and sorry for the trouble. As described, when I digitally sign a document in Reader.  Reader states that "the document has changed after signing.

     

    Is this a behavior with a particular PDF file or with all the PDFs that you digitally sign? Please try with a different PDF file and check.  If the file is stored on a shared network drive, please download it to your compouter first and try signing it and check.

     

    You may also try to sign the PDF file online via Document Cloud https://documentcloud.adobe.com/link/home/ and see if that helps.

     

    Regards

    Amal

    S
    SeamountainAuthor
    Participating Frequently
    October 22, 2021
    556 / 5000
     

    Översättningsresultat

    Hi Amal,
    It does not matter if the document is stored locally on my computer or on a network device, I get the same problem with Adobe saying that the document has been modified, with the result that the signature is invalid.
    I did not test to sign online because it is not an alternative for me.
    I have seen some posts from 2017 about SHA1 and SHA256 and if I change the windows registry so that Adobe will use SHA1, I will not get the error that the document has been changed.
    So what is it that makes Adobe think the document has changed if I use SHA256?
    S
    SeamountainAuthor
    Participating Frequently
    October 27, 2021

    Most 3rd party signature validators only check the cryptographic validity of the CMS signature, and may also check the revocation status of the signing certificate. Acrobat, in addition, performs "Document Modification Analysis" to detect changes to content or field values that may cause the signature to be declared invalid due to "document has been altered or corrupted since it has been signed". The CMS signature may be valid. Adobe has not, to my knowledge, documented the internal checks that Acrobat and Reader make to reach that determination. It's more complicated than you might think.


    Hello,

    My next step will be to do a new installation of Reader to see if it makes any difference and I keep my fingers crossed that it does.

    Are there any special Reader settings I should check? I found a page on Adobe where a lot of Registry keys were described but it is difficult to control something when you do not really know what to control.

    I also do not think I use an "evil signing program" as I use the feature found in Reader, and in Pro. It's probably Adobe itself that created that function, so they should do it in a way that they themselves think is okay.

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