As of a few days ago I'm unable to sign any PDFs in the normal manner. I normally use 'Digitally Sign' as follows. Highlight where the signature field goes and wait for the dialogue box to appear for the password. Except it doesn't appear and the Acrobat window greys out (I can just see the signature marquee, so it's semi-transparent, fwiw I uploaded this) and key inputs are bonged. The only way out is to 'Esc'. I've rebooted PC (running Win10). Checked for updates - it's up-to-date. Manually repaired Acrobat. Searching the community doesn't reveal anything that looks useful. Or IT guru can't help although notes that he's had several users with strange, but not identical issues. I tried 'Fill And Sign', Request Signatures. The resulting dialogue box appears but is empty and white. Stamp Tool works.
Hope you are doing well and sorry for the trouble. As described you are getting the black screen when trying to sign the PDF file.
Please go to Edit (Win) > Adobe Acrobat (Mac) > Preferences > Signatures > Creation and appearance > Click More > Uncheck 'Use modern user interface' > Click OK and reboot the computer once.
I tried this for the same issue and nothing changed. Is there a new workaround?
I followed the approved answer, above, at the time. It worked. I just looked at my current setup, which is also working fine and the tick box is checked.
Version: 22.1.20117.0 is my current verison.