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Seamountain
Participating Frequently
October 22, 2021
Question

Digital Signature. document changed, invalid signature.

  • October 22, 2021
  • 1 reply
  • 19668 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.
    Community Manager
    Amal.Community Manager
    Community Manager
    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?
    M
    margueritek
    Inspiring
    October 26, 2021

     Indeed, apparently your Acrobat installation succeeds where your Reader installation fails.

     Maybe some Reader settings are broken (you may try to compare configurations; but the configurations you can view in the Preferences dialog is not complete, much is only in files or the Registry).

     Or maybe the installation is broken (you may try to uninstall and re-install the Reader).

     Have a look at the versions, though! Your Reader has version 2021.007.20091 while your Acrobat has 2020.004.30015. In the worst case a bug found its way into the Reader in the time between which results in the observed behavior...


    There are some theoretical exploits, generally involving invalid objects and misuse of white space, which I have never seen in real life. Rewriting all the unsigned incremental sections (including the linearization section) prevents these exploits (unless you have an evil signing program).

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