I have several different Book projects and the largest is 49 MB. When I update this Book project, which I do about once a week, it takes a long time for the project to open and I sometimes get the spinning ball for 10 to 20 seconds. After it opens, I'm able to successfully overwrite the existing PDF file and everything appears to display correctly. Is the Book project file getting too large? If so, is there something I could do to compress it?