I am doing metadata auditing for government documents these days and there are UUIDs in lots of files going back a very long time. I have certainly seen them in PDFs and Word and Excel documents that long predated the current AI integrations.

Edit to add: I just tested LibreOffice/26.2.5.2 and it is not injecting a UUID into the metadata either for a ODT or a DOCx (2007) file. I do not have native MS Office available on hand to test at the moment. I do see these UUIDs in published government documents but cannot swear to exactly what step of the pipeline is stamping them. Definitely on files that predate the AI integration push by Microsoft.