I hired a guy to draw some custom models for me. They are in .obj format. I can't import them. When I try to drag and drop, I get an error message; when I try to choose them from my hard drive, they are grayed out/unavailable for selection.

I'm using Version 5.2.1 Mac App Store.

He has sent me screen shots indicated they are working correctly on his end.

Can anyone help me understand the problem?