Purchased version of Adobe Acrobat DC now requiring subscription?

[Richard5E61]

I have a purchased (non-subscription) version of Acrobat DC 2017 that I downloaded a several years ago that has performed wonderfully for years. I'm now getting the following pop up messages that ultimately require me to enter a serial number that I don't have and can't find.  My Adobe account shows no record of my registration of this software. Can anybody help me out?
I've been getting the following screens:

When I select "License This Software" I get this.

Then this

Thanks

Rich