I assume you have considered OSMAnd~, and the openstreetmaps were unsuitable? I was not aware PDFs could have geo coords for what you describe. Sounds useful though.
Might want to cross-post to !foss_requests@libretechni.ca. It’s a ghost town but at least your request would sit at the top of the stack for a while.
Could increase your reach by crossposting to these places as well: