Hi Ted,
I used to use PDF's but switched to using Book resources for a couple of reasons. One, PDF's were much more time consuming and awkward to edit and update. Two, there was no simple way to create a link/path to another PDF, reading assignment, or directions.
Using Book's had multiple advantages. I could edit, if needed, right in Moodle. I could break up long PDF's by splitting into chapters and sub-chapters. And the one you need, I could enter HTML links that would take my students directly to the next needed location in the course. Just go to the location I wanted to go to, copy the URL, go to the point in the book where I wanted to jump from, insert the URL link, then save the book. In many cases, I would have multiple links since I taught 7th and 8th graders, and depending on the grade of the student, they would need to jump to different places, sometimes.