I independently "invented" this 2 months ago, also for parsing 100 page long PDFs. Give each page a title and summary, but prepend as context the title+summary of previous 3 pages. In the end combine all titles+summaries to get a master index using the LLM. At runtime you first use the index to zoom into the desired sections to give the answer. I think this makes the RAG "smarter", not based on simple similarity.