Buying a pdf ebook is never a great idea. If you want to try to fix it you're going to need to strip the DRM. That's possible, but you'll need to Google the appropriate info, 'Adept DRM' should put you on the right track - there are different scripts for pdf vs. epub, you need the pdf variant.
In terms of converting it, see here for what you're up against:
http://calibre-ebook.com/user_manual...-pdf-documents
In other words it's likely that it still won't be pretty, but you will then have the ability to fix it yourself at least.