Well mostly I guess that the first part has to do with checking that the end of one page matches the beginning of the next, and makes sense (the "makes sense" bit probably can't be brute forced) - 100! is probably not easily brute forceable either - but I suspect that this is really a process something that might not actually be strictly factorial in nature.

But once you've done that I think there's an actual mystery to solve as well - probably something that requires an actual human to read it