is there any EPUB library ?

Well, seems like you might need an SDK to create your own reader, I don't think there's another way out. While there're some open-source libraries usually they lack of support and further development. So, if you're targeted to create a standalone app for iOS, Android or Xamarine you could try e. g. https://epubear.scand.com/ . It goes with a 1-year license, 1 application and they even provide cloud hosting for all the books you collect with complete DRM. And the team is easy to get in touch with. )