My acrobat app crashed the other day and I couldnt get it to open at all. Managed to get it closed but now the 'Open' button is greyed out. I've tried uninstalling it and loging in and out of creative cloud and nothing as helped.
Can you open it from the Start menu (I assume you are on Windows)? If that does not work, what about navigating to where it is installed in c:\Program Files or Program Files (x86) and starting it from there? (use e.g. c:\program files\Adobe\Acrobat <version number>\Acrobat\Acrobat.exe)