Why is my digital signature not trusted in Adobe Reader?

Why do I get an error message in Adobe Reader when I open a signed document?

The error message in Adobe Reader states:
"The validity of the document certification is UNKNOWN. The author could not be verified. At least one signature has problems."

Signature trust error in Adobe Reader.

If you are using an older version of Adobe Reader, it will not automatically recognize your signature. To resolve the issue:

  • Update your version of Adobe Reader; or
  • Update Adobe Reader’s trust list.

Update Adobe Reader

Update Adobe Reader.

To update your version of Adobe Reader:
  • Click Help on the toolbar.
  • Click on Check for Updates.

Update Adobe's Trust List

Update Adobe Approved Trust List (AATL).

To update the Trust List:

  • Click on Edit on the toolbar.
  • Click Preferences… on the dropdown menu.
  • The Preferences window will now open. On the left-hand Categories list, select Trust Manager.
  • On the Automatic Adobe Approved Trust List (AATL) updates panel click the Update Now button.
Adobe Reader will now automatically trust your digital signature.