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.
In this case: Institutions of power in the intelligence, military, foreign relations, etc. People and groups, institutions and interests ensconced in elephantine bureaucracies that actually make things happen and are kind of a backstop to power. They're the violence that doesn't answer to the state as liberals presume they should, they do obey orders of the state in so far as the state's interests are theirs but also slow-walk, sabotage them, avoid them, go around them, and if really necessary disobey them directly if they deem it necessary. They're the people who will kill a sitting president, the people who smuggle drugs in for off the books revenues to use on operations without pesky congressional or executive branch oversight. They are the inertia, the institutional guarantee against changing of whims among the elected congress-critters and changing seats in the white house and even in appointed offices like heads of say the CIA, FBI, joint chiefs, etc.
The deep state is everyone from career CIA, NSA, military, foreign policy managers and mid-level agents and personnel who work on the clock completely above board and who can resist any dramatic changes simply by continuing to pursue what has been deemed better, to pursue what they believe and have been led to believe is the right course to shadowy groups of intelligence adjacent types who in addition to funding in theory subject to audit in the intelligence black hole funding bag also have access to off the books funds, the types who kill people and break laws and rules, who answer to no elected persons and are in every way that matters immune to consequences save from among their own. They do things like MKUltra, run Epstein child trafficking rings to traffic victims for compromising material to leverage against government and business leaders and to gain their favor so they don't even have to use pressure.
This sprawling apparatus both the submerged "deep" parts and visible parts is why those boat dealers were able to waltz into congress on Jan 6th without resistance but a confused two people in an SUV who took the wrong highway exit to the NSA and panicked, running the checkpoints instead of stopping were shot dead with automatic weapons fire before they got anywhere close to it without asking further questions.