OK, so I am a 3rd year student @ UTDB. Here is my advise.
Direct answer to your question about PDF is that IBooks can import PDFS for viewing by using Dropbox, which I mention below. This allows you to do what you want for FREE. iBook turns them into books. Very handy. Below is a list of some of the programs that I ave found to be useful during dental school.
1)Powerpoints- Keynotes I have both Keynotes and Docstogo and I find that keynotes is by FAR the better product.
2)Note taking for class- Noteshelf (get a stylus) or if you prefer to use a BT keyboard get iDO-notepad. Moving files from home computer ect. Dropbox.
3)Drug Handbook- Lexicom- what ever you can afford. This app is awesome (I have the $199 version) it will save you a LOT of trouble looking up natrasuticals and pharm interactions when you are in Oral Sx.
4) Gross anatomy- Netter's Head and Neck can't be beat! Rohen's Anatomy is also very useful because it has actual pictures of the cadavers.
5) OHI instructions for Pt.s (patients) get Cavity Free 3D free and useful.
6) Pt education: DentALL, Orashere, Checkdent Pro, ToothIQ are all very good for different things.
7) Obscure disease names: Eponyms very useful!
8) Refresher for CPR: CPR-Chocking from AHA. Very useful for review.
9) Oral Sx: Sutures- shows how and when to do different sutures. Trust me this one is a life saver!
10) Spanish: Dental spanish- this program is very useful in the south where I am.
I hope that you find this to be useful!