Originally Posted by KMvBC
I have a number of eReader apps on my iPhone and iPad (iBooks, B&N eReader, Kobo, Kindle, and I just downloaded Stanza) which I would like to get the books from those apps to the Calibre library.
One approach for B&N, Kobo and Kindle is to download the same files either directly from your store account to your PC or Mac (B&N and Kobo) or to their PC/Mac app (Kindle). These ebooks will typically have DRM (encryption), and in the case of Kobo and Kindle this means that the files won't be (or might not be) the same as on your iThing because of the encryption. See Apprentice Alf's Blog for more info about DRM.
Once the files have been downloaded they can be imported into Calibre via Add Books. The K4PC files will be in My Documents\My Kindle Content and K4Mac puts them in 'username'/library/application support/kindle/my kindle content