Register a digital ID

I have a military CAC with digital certificates connected via CAC reader to my Mac.  I am able to access all CAC-enabled websites.  However, I am no longer able to use it to digitally sign pdf's in Adobe Acrobat Reader DC.  It does not seem to recognize the CAC.  I have tried to "Add Digital ID" per the website (https://helpx.adobe.com/acrobat/using/digital-ids.html?mv=product#register_a_digital_id) but I run into a similar problem:  "Adobe Acrobat could not find any new digital IDs."  Screen shot attached.

How do I get Adobe Acrobat to recognize my digital certificate?