Hello Timj,
We're sorry for the trouble you had with the Adobe Reader DC. Please reboot the machine once and then Sign out and Sign back in Adobe Reader using your current Adobe ID and password.
If it's not letting you sign out or sign back in, then reboot the machine again, try resetting the Adobe Reader's Preferences once, to reset the Preferences, refer to the steps mentioned in the article How to reset Acrobat Preference settings to default.
Reboot the machine and then sign in Adobe Reader and check
If you still experience any issue, then use Acrobat cleaner tool to remove Adobe Reader from the machine Download Adobe Reader and Acrobat Cleaner Tool - Adobe Labs
Reboot the computer and install the latest version of Adobe Reader from Adobe - Adobe Acrobat Reader DC Distribution
Let us know how it goes and share your findings.
Thanks,
Anand Sri.