If you don’t even trust the teacher to be able to open a PDF, I’d probably be more concerned about them opening the .docx file with Microsoft Office 97, or whichever archaic version they have always used on their PC, and ending up with a completely broken assignment.

Edit: Sorry I misread your comment, you talked about the process of digitally grading a PDF, I was thinking of the process of simply opening a PDF.

That’s exactly what it is. I haven’t looked into it too much, but as far as I know it’s main advantage is simplifying the setup process, which in turn reduces the chances of a misconfigured VPN.