Opening a PDF now requires Microsoft sign-in

Suddenly when I try to use Acrobat reader (on my desktop Mac), a pop-up window requires me to sign into an old Microsoft account which is no longer active.  When I try to sign in with my current Microsoft account, I get an error message and I can't go any further.  However, I can't close out the error message.  I have to Force Quit Acrobat.  So now I can't open PDFs.  Why do I now need a Microsoft sign-in?  And how can I get it to recognize my current account?