I've deleted the account that originally created the authorization for Digital Editions, but it requires me to sign in with the account to delete the authorization, but the account doesnt exist anymore, and even deleting the app and reinstalling doesn't get rid of the authorization.
I/m on a macbook air running macOS 10.12.1 and Adobe Digital Editions 4.5.2
this answered it for me.
quit Adobe Digital Editions.
Navigate to /Users//Library/Application Support/Adobe/Digital Editions and drag the activation.dat file to the trash.
If you are using 10.7, see https://helpx.adobe.com/x-productkb/global/access-hidden-user-library-files.html
Open Adobe Digital Editions and reauthorize.