If you are not familiar with OneNote, you can use it to create a hierarchical structure similar to a directory tree, except that anything that you select at any level shows text. It seems like the perfect way of organizing chapters and subchapters of a textbook.

I don’t much enjoy saying nice things about Microsoft products, but OneNote seems to me to be the best of this class of program, which is unfortunate because there is no free read-only version of OneNote. With OneNote, you could have the chapters appear on the top and, once you select a chapter, you could see the subchapters listed on the side. It would make it very easy to jump back and forth to different sections of a book. This is not something that you would likely do for a novel, but would be handy for textbooks or any other instructional text.