Funny, we get more complaints about DuckDuckGo browser than anything else, and that’s one of the few we don’t test on. I know this because I make it a point to have someone from CS tell me about consistent pain points users are having. I wonder how many complaints about Firefox not working your customer service team is getting daily and you just don’t hear about it because they’ve been told to tell users “just say Firefox isn’t a supported browser and to try installing Chrome.”
You should ask someone in CS. Whichever agent bullshits the least (not the manager) - you might learn something.
Almost 3/10 people accessing your sites are using Firefox. All those “images not loading right or whatever” are probably blatant to them, making them think “wow, what an absolute shit website.”
3 out of 10.
Unfortunately that wouldn’t work as this is information inside the PDF itself so it has nothing to do with the file hash (although that is one way to track.)
Now that this is known, It’s not enough to remove metadata from the PDF itself. Each image inside a PDF, for example, can contain metadata. I say this because they’re apparently starting a game of whack-a-mole because this won’t stop here.
There are multiple ways of removing ALL metadata from a PDF, here are most of them.
It will be slow-ish and probably make the file larger, but if you’re sharing a PDF that only you are supposed to have access to, it’s worth it. MAT or exiftool should work.
Edit: as spoken about in another comment thread here, there is also pdf/image steganography as a technique they can use.