Unable to open files

Can you try the following steps and let us know if it works :-
Is there any other Adobe app on your device? If yes, can user try to logout from all Adobe apps from his device and then login  via Acrobat app ?
Is there an Adobe accounts in Android Account settings ? Can you please remove the Adobe account from the settings and then login again in the app ? https://support.google.com/android/answer/7664951?hl=en
Thanks,
Acrobat Android Team

Please be more specific. Are you using the Acrobat Reader mobile app?

And when you say that you're not able to download, where exactly are you trying to download files from?