If you add markers to a document, then the markers basically become the pages. You can use the Next/Previous Screen actions instead, which will not be affected by the markers.
However, I can't really recommend your approach of putting all your songs into one long PDF instead of setting up individual songs in the app. I don't know what advantages you're getting from doing that, but it will defeat a lot of the functionality of the app, like the ability to auto-scroll the documents, play a metronome with each song's tempo, or jump around to different songs while rehearsing.