Tofu [OS X] is a really nice way to make long pieces of text more readable on screen. Drag in a text file (for example, the full text of Erik Benson's book 'Man Versus Himself', or one of the many files from and Tofu displays it in newspaper-style columns. One of the reasons I enjoyed reading Cory Doctorow's book 'Down and Out in the Magic Kingdom' so much was the 2-page PDF layout - just like reading a book, you only had to move the page every now and then, and could keep the whole contextual surroundings in view.
Tofu doesn't handle PDFs, at least not yet, but you can convert them to RTF with TextLightning first. AntiWordService should be useful for Word documents.