Welcome to CNET Australia's App of the Day, where you can see some of the coolest, silliest and most useful apps in action.
There are a lot of PDF readers on the iTunes store. You might be tempted by one of the free ones, which is fine, if all you want to do is read your PDF files. However, if you want to do more, I'm afraid you're going to have to spend some money. One of the best I've seen has to be GoodReader. It's really easy to use, and comes with a whole bunch of mark-up options, including highlighting, text options, sticky notes, lines, shapes and free drawing. I also really like how it offers to create a copy for your annotations, so that the original PDF document remains intact if you need it to.