A long time ago, I discovered a bunch of websites that had their search bar feeding back your previous searches as suggestions. You would for example search for

A long time ago, I discovered a bunch of websites that had their search bar feeding back your previous searches as suggestions. You would for example search for "abc 1234 xyz 2345" once, and upon next search, typing "abc 1234" would then suggest "abc 1234 xyz 2345". You can probably guess where I'm headed now and in a true "if it can be done it has to be done" mindset, subsequently had the most fun implementing a parasitic KV-storage engine on top of those search bars. I was probably prouder of it at the time than I am now, and would today strongly recommend against storing your PDFs in other people's search bars. Obviously can't know for sure if this is what's happening here, but seeing this definitely rings a bell.