Take a look at the REMNux reverse engineering page for PDF documents (https://docs.remnux.org/discover-the-tools/analyze+documents...). Lots of tools here for looking at malicious PDFs that can be used to inspect/understand even non-malicious documents.

In what contest do you use that tool? Looks like that page is primarily about editing pdfs using that format rather than inspecting.

Very tempting to fool around with the ideas especially after the Epstein pdf debacle.