This.Your inability to read is very disappointing.
Even if the button isn't there, so long as you've viewed the file (and tried to download it?), if you return to your Drive, and go to your "Shared with me" section, it'll appear and you can make a copy. It's the most sure-fire method there is. Learn how to read, and furthermore, be sure of your shit before trying to throw it at somebody and have it thrown back at you.