I am unable to sign documents with my digital certificate.

Hi ​@cleia_6776 ,

Is this happening with just one PDF or any PDF that you try to sign with your digital certificate?

What happens if you manually update the  Adobe Approved Trust List (AATL) certificates?

• Go to Preferences ==>  Trust Manager ==> Automtic Adobe Approved Trust List (AATL) updates ==> tick the checkbox “Load trusted certificates from Adobe AATL server ==> click on “Update Now button”

Is your Acrobat Pro updated to its most current version?  If you’re on Windows, what happens if you repair your Acrobat installation?

@cleia_6776 essentially nothing happens? Maybe it's corrupted preferences. I had to remove my Preferences from my MAC, which oddly was over 17 gigs and once I removed it, it was a merely 384kb! If I look at it now, it's only 409kb! I did a search for my preferences, and on my Mac, it's in a folder on the Hard Drive - Library - Preferences. Apple had told me to remove all the preferences (delete them); I was skeptical, so, I made a duplicate copy to my desktop of the whole folder of Preferences — and then went back to the Library - Preferences, and selected everything inside and deleted it. Once, I did that, I restarted my computer, because it will create a new set of preferences, and launch Acrobat, and it worked fine.