Let's say, as an example, that I want to create a GPT using a book from 1921 that is now out of copyright. I upload the book, but it doesn't really seem like GPT is reading through it, digesting it, and performing quick data usage. Any function using data from the uploaded book seems to take a long time, and it doesn't seem as if GPT natively understand it all. Is anyone having success with this, and if so, how? There are many custom GPTs that I have ideas to create, but they all require incorporation of the data into the fast recall responses.