I'd like to update a previously-published book but I don't have the original file.. was done on a friend's Mac and seems to have been lost. I have however bought my own copy of the book. How can I retrieve the ibooks author file from the published copy?
That file is just a zip file. Authors can rename the suffix and unpack to browse some of the assets, but if you want to reverse engineer your own book you'll need to start over in iBooks Author and do that manually.