Open iBooks files in other PDF viewers in iPad iBooks permits easy file sharing and import of Pdf files to iPad through iTunes, however it lacks annotation/highlighting. After import, I prefer to open PDF file with 3rd party PDF viewers like Foxit. However I have no idea how to bring my PDF file from iBooks to Foxit reader. 

Do you have any idea?
I'm afraid it's not possible. I tried several times to do that.
Maybe you'll want to use an app like Documents by Readdle on your iPad? That way you can manage your books from there and open them everywhere you want to.