Just as a contrapoint to the other commenters, I've had Mac do this on PDFs that I myself scanned many years ago. Pretty sure they were not malware.

I suspect what triggered it was the fact that the files had journeyed through many filesystems in their time - HFS, ext4, NTFS, APFS - and they probably picked up some unholy combination of impossible attributes.

I thought it was pretty egregious to have Apple helpfully try to delete important PDFs that I've been lugging around for years.