I have a persistent problem with Acrobat Reader on Android, and its interaction with Dropbox. If I open a .pdf from Dropbox in Acrobat Reader, and then make annotations in it in Acrobat, the result is *never* saved automatically. If I want it saved, I have to manually "share" it to "add to Dropbox" etc.
My understanding is that it ought to save automatically, and that this is the point of Adobe/Dropbox integration. I'm running Android 7.1.2, with the latest versions of the Acrobat and Dropbox apps. Does anyone else have this problem?