google play book add

hi, i wanted to add some of my favorite books that are not in the market such as the once and future king, etc... ive been playing a while and really like the read aloud feature and have been looking for apps as polished as play book with the read aloud. is there any way i can add my ebook file i downloaded to it? ive been trying to find the right place to drop the file in with no luck.... please let me know thanks!!!