I make eBooks in InDesign in PDF format, and they are huge. 800 pages, for instance. All about various digital cameras.
My readers are faced with this issue: it's huge, much larger than can be absorbed at a single sitting. Can they pick up reading where they left off? Of course, they might remember the page they last visited, and pick it up there, but is there a means where their computer will remember where in the large document they were last time it closed, then open it back up at that spot?
For all I know, this is Reader 101, but I don't find anything like it in my research.