Well, you can first import the PDF into the library. Then open the note you want to import it into. Go to Edit Pages in that note. Press the menu button and chose Copy from other notes. Choose the PDF that you imported and then select the pages of the PDF and hit copy. This will insert all the selected pages into your note.
The only thing is that I don't see a Select All option there, so you have to checkmark each page. That can be done quickly, but if you're taking about a 300 page book, that will be a bit tedious. A 50 page PDF though is not bad.