I'm studying to get MSSQL Server certified, and I'm reading eBooks to do it. I have a company login to Books24x7 which has books online, but I can't download the whole thing, and switching between books loses my place in a book. I got my hands on some PDF versions of books, and I am reminded that reading a PDF designed as a printed book is not nearly as convenient as reading, say, a web page or Word document (not in layout view).

Then it occurred to me to see if Acrobat Reader had some function to re-flow the text to make it easier to read electronically. Whaddayaknow, View -> Zoom -> Reflow does exactly what I wanted. Now I'm reading an e-book reflowed to fill my window much like a web page does. (Well, a web page without ads and navigation columns.)