how do i close the blank window without force killing?

Problem using the Adobe Reader DC

I clicked on "share", but this blank window popped up. I couldn't close it or open another document. Task manager shows Adobe Reader running fine.

Is there a way to close the blank window without force killing it? I need to save this document before exiting the program. Your help is appreciated!

[Moved from Community Help (which is about the forums) to a better forum... Mod]
[To find a forum for your program please start at https://community.adobe.com/]