I've been using iBooks since the release of Mavericks, and it has worked as it should until today. Today, I added a PDF file that I had edited in Preview (added notes, and red lines to my own homework), and now it won't open! Whenever I attempt to open iBooks, it just says: "iBooks closed unexpectedly." and gives me the options to ignore, send to apple or try again. It's quite frustrating because my files in iBooks is something I am using at my university and they include my important notes as well. EDIT: I've installed Mavericks on top of Lion and not Developer Preview.