This month we’re showing you calibre. calibre is an “iTunes for e-books”. Electronic books can be organized and, much more importantly, converted to many formats. This way you can read all your e-books on any tablet or an iPad.

Why does iBooks dictionary lookup not work?

iBooks dictionary and highlight feature is only supported in “real ebooks”. Every PDF e-books has to be converted to ePUB — with calibre for example — before the features work.

http://www.free-mac-software.com/calibre