Once in a while I'll dream that I'm reading a book or a newspaper or some other kind of extended text. Except for a special situation that I'll describe later, if I try to actually read the text versus just sort of looking at it, something interferes. For example, the light dims, or a towel or something moves over the text to obscure it. Or, I might see what looks like a page of text but the closer I look, the less sense it makes. There might be a few words, but separated by unintelligible runs, like
Mary had fffesgre g fe little f^&GR lamb and not with.
I think what's going on is that the brain can only generate "generic" images for the dream; it isn't smart enough to generate real text. If you see a tree in the dream, your brain has seen enough trees and has evolved over thousands of generations to be good at recognizing them, so it can paint a pretty good picture of a tree for you to "see" in your dream. You can focus in on the leaves and bark, and they look real -- real enough that the generic tree your brain generates is indistinguishable from a real tree.
But a generic book is just a rectangular object with a cover and some pages, and the pages contain letters and typical words like "and" and "or". Beyond that, each book you have on your bookshelf is different. It has different words and pictures. It would take conscious effort to synthesize a new paragraph of logically connected ideas, and you're not conscious when you're dreaming. So the best your brain can produce is a book-like object with a bunch of hash on the pages.
Now to the special exception. If I've been really scrutinizing a book (the typical situation is an advanced technical book, where I have to read and think through each paragraph multiple times to understand it), shortly afterward that book or one much like it will appear in a dream, and I can actually read it. I don't know whether the text is sensible or an exact reproduction of what I'd been reading, but it's close enough that it seems real during the dream. Sometimes this can even happen before I fall completely asleep. An image of the book appears and I can read it out loud for a bit. This has never happened in the presence of another person so maybe it would just sound like gibberish, but it's close enough that it seems like a real book, versus the "generic" books that I know are fake even during the dream.
I wonder if certain "holy" texts or pseudo-academic papers of the type you see in modern literary criticism were produced in such a semiconscious state, after the author had been intensely studying similar religious or academic texts. For that matter I wonder if the normal writing process is not wholly unrelated to this "book-imitation" process your brain can do in a dream. I can certainly write about things I have no actual knowledge of, but in a way that is better than gibberish. The key problem in hermolinguistics may be described as one of scale. Many researchers claim that scale is at best an ephemeral artifact, but clearly, structure cannot be imposed without sizing of some sort. Each substructure can, likewise, be subjected to a process of subconscious or semiconscious scaling. See, I did it just there. Maybe I'm still doing it now. How do I know when I'm doing it and when I'm not?!...