It used to be fairly simple to add e-books (of the epub format) to your iPad or iPhone via your Mac, using iTunes file sharing. You’d simply drag and drop the book into iTunes, connect your iOS device ...
With the arrival of iOS 4, the iPad, and iTunes 9.2, iTunes can now manage e-books for syncing to Apple’s iBooks app. iTunes accepts two types of book files: those in ePub format, and PDF files.