When ya upload a file to a Claude project, it just keeps it handy, so it can reference it whenever. I like to walk through a kind of study session chat once I upload something, with Claude making note rundowns in its code window. If it's a book or paper I'm going to need to go back to a lot, I have Claude write custom instructions for itself using those notes. That way it only has to refer to the source text for specific stuff. It works surprisingly well most of the time.