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I have the same problem. I did a deregister and erase of my Nook HD. Now Acrobat DC won't let me sign in.
Perhaps it is related to another problem ---- Adobe Air was reset to version 220.127.116.115. I can click on "Update" in Google Play and the latest Adobe Air 17.xxx downloads, but then it gives and error message of something like "already installed" and won't update.
Any word on solutions for Acrobat DC or updating Adobe Air?
I have the same problem. When I try to turn on mobile link I am redirected to the sing in/sign up screen and no matter whether I tap 'sign in' or 'sign up' nothing happens. It looks like those buttons just don't work