If the goal is to have documents that cannot be edited, then the docs should be printed and submitted. Hardcopy. Otherwise, anything can be edited.
If the goal is to make it reasonably hard to make changes so that the vast majority won't try ... just require everything to be submitted as PDF. Or, if it's a presentation, as some kind of movie file.
Otherwise, you end up with this kind of confusion. And, honestly, not being able to open the most common document format on the planet seems rather lame.