PDF Random Accessibility

Here’s a funky one… one of our clients publishes a 50+M pdf file periodically. Now they need approx. 200 users to view specific parts of that file, without ability to view remainder.
Has anyone ever heard of a way to do this? If one user needs to view all of the bookmark “x”, how do I keep them from seeing “y”?
This needs to be based upon user permissions.
Any ideas, short of busting the parent file into 200 discrete pdfs?
Thanks!
Chip