Select Default PDF Handler is grayed out

I have Acrobat 10 Pro and Acrobat Reader DC on my work computer. My supervisor needed to show me something she was working on, on my local machine and signed into Creative Cloud on my machine. It wanted install files, so I let it. When she was finished showing me what she needed to show me, I could not open .pdfs unless I logged in with her credentials. I don't have her credentials, so I uninstalled Creative Cloud. Now I can't open .pdfs unless I open Acrobat 10 Pro and browse to them. I don't want to do that; also I can't open more than one .pdf at a time like that. I have tried to change the default .pdf on my machine, but Acrobat 10 Pro does not show up on the list of available software. I tried to change it through Acrobat 10 Pro > Preferences > General, but the Select Default PDF Handler button is grayed out. What do I need to do to make Acrobat 10 Pro be the default again? I am administrator on the machine.

Thank you.