I keep computer science/math-related PDFs in Dropbox, copy them to GoodReader (I've started experimenting a bit with other PDF apps, but GoodReader has been my go to for years now), and occasionally use Apple Pencil to mark them up as I read them. I don't save them back to Dropbox for future review; GoodReader is effectively its own island in that regard.

For GPS, I use Gaia GPS to create routes, often with Apple Maps and/or Google Maps running in split screen.

If you have specific questions, I can address them, but none of it is particularly formal.