Adobe Acrobat Reader PDF Error: "At least one signature is invalid."

Issue

I received a PDF that has a banner at the top saying, "At least one signature is invalid". How do I fix this error?

Explanation

Adobe does not recognize the certificate used for one or more of the signatures in the PDF. Commonly, this is because the signer used the UTD-issued certificate they got by following CKCS #180: Digital Certificates. If you are the recipient of a PDF that was signed using a UTD-issued certificate, you will need to "trust" UTD's main certificate (the one all individual UTD certificates are validated against) in Adobe.

Trust the Certificate

  • Click the Signature Panel button in the banner where the error is.
  • Then, click on the Signatures iconin the left-hand sidebar.

Signature sidebar with signatures button depicted by pen icon selected.

  • You will be able to see all the signatures which are causing the issue. However, you need to validate only one signature to remove this error.
    • To do that, expand a signature and then the Signature Details section by clicking the arrows adjacent to them. Then, select Certificate Details.

Signature sidebar with a drop down list for the selected signature showing the signature details, including certificate details.

  • Select the row above the one with a warning sign in the new window. The row should state "The University of Texas at Dallas RSA".
  • In the window, navigate to the Trust tab and select Add to Trusted Certificates.

Certificate viewer window with Trust tab selected to display the Add to Trusted Certificates button at the bottom.

  • Select OK in the first dialog box after reading the instructions displayed.

Acrobat Security dialog box confirming the choice to change the trust settings.

  • In the Import Contact Settings window which opens next, check the option "Use this certificate as a trusted root".
  • Select OK to close all windows and finish the task.

Import Contact Settings window with check box to use the selected certificate as a trusted root.

  • Close the document and reopen it. You should not get the error again.

Details

Article ID: 231
Created
Mon 11/22/21 12:45 PM
Modified
Wed 12/20/23 3:07 PM