Imagine getting arrested in a non-eyes, non-NATO country by the US. And right on the doorstep of Vietnam and China. How does that even work? Did the Cambodian authorities for some reason agree to arrest a dude who was in all likelihood an undeclared spy in their country for the benefit of the US and just hand him over without any further questions? Did the CIA kidnap him onto a plane and drag him away? Did he agree to be arrested and cooperate? I mean it’s right next door, a bus ride to Vietnam and a short plane jaunt to China and absolutely beyond the hand of the US.
Also kind of funny, I thought at the time that the leak was almost certainly done by the administration itself to try and tamp down the back and forth between Iran and the zionist colony and prevent a war they didn’t want to be in.
Failing something like diffing which is the best way you might consider a tool that enables you to print the document contents to another document, either another type of document (epub to pdf for example) or the same type and doing that should result in no metadata at all carrying over. Of course you need the right tool for it and it may result in all kinds of mishaps with shifted text and pages and other nonsense so diffing would be better while this printing to another file solution would be nuclear but likely to foil everything but very advanced methods not likely to be employed to prevent piracy and basically impossible to automate.
I’d open the files up in Calibre or another viewer and see what kind of info it shows. Try to strip that, then open the result in a hex editor and try searching for your registered email address or phone number within the file which is the low hanging fruit obviously as if I were Amazon I’d use an internally known account number in either plaintext or even better encoded in unprintable bytes. All in all I’d try the printing to/converting to another format trick or consulting people more knowledgeable about this about methods and what to do.