Even Microsoft Word stores revision history inside .docx files, and that’s been used to expose plagiarism. I heard about one case where a student took an existing paper (I believe from a previous year/student) and pasted it into Word. They then edited it just enough to make it look different.

However, they didn’t remove the embedded revision history in the .docx file they submitted, so that went about as well as you can expect.

Are you sure about that? I could easily see this happen with a web document link, but for a docx file the change tracking is off by default and pretty obtrusive. Basic metadata would be fine, formatting might be quirky but that's not exactly a smoking gun...