I'm not sure why anyone would put a book in an epub format, but unfortunately I purchased several books that are in that format. I have digital editions content under an ID I don't remember. All my content should be under the same ID but when I try to access the content i receive a message asking me to enter my email address and content code. Where do I find this information?
FXL ePubs and Reflowable ePubs (and mobi for Kindle) are very popular for books. If you are on a Mac or iOS device, such as an iPad, the iBooks reader is very good for reading ePubs.