Another possibility is to put the variations in a worksheet (where you can also calculate the answers in a second complementary worksheet) and associate each variation with a student and use mail merge to create a custom version of the question paper for each student. That would also make it easier to add mutiple questions. You can then compare the student's answers with the question sheet and more easily identify where the plagiarism comes from.

You could mix a few fixed questions with the random questions (especially the first questions so the plagiarists may not immediately notice)

__________________
Graham Mayor - MS MVP (Word) (2002-2019)
Visit my web site for more programming tips and ready made processes www.gmayor.com