Hi stephy, just wondering what password protected books you are trying to open on your iPad? A little more information would help us out here in order to help you.
You can use such apps, like Bluefire reader which is free to read your Adobe digital rights management PDFs. I also would suggest to get the app called Overdrive as many local libraries use this app to read these types of Books. I have used overdrive myself when I check out books from my library, works well and is also free.