No problem: en.wikipedia.org/wiki/Common_Access_Card

Essentially it’s a physical token containing a certificate. I can then put that card into a CAC card reader and authenticate with it and a PIN that I setup on my card.

I can then also sign PDF signature blocks with the cert on the card. I have only found this ability in Adobe Acrobat. The signature block in Adobe is different from just their regular sign location for digital ink. I’ve never made a PDF with one of those blocks, I’ve only just signed them so I’m not sure what exactly that kind of signing block is called.

So bottom line, it’s a physical card with a certificate loaded on it. Adobe can read that cert and use it to sign signature blocks inside a PDF.