In the beginning of the The Post, you see that the people leaking the Pentagon Papers cut the page numbers off each page before they copy it. Why did they do this? For anyone - including investigative journalists - finding the material, it is hard to figure out in which order the pages were.
In fact, that is making Ben Bradlee (Tom Hanks) and his journalists team a lot of trouble when they receive the material later in the movie, because they have to order thousands of pages without any of them carrying a page number.