4. Though Mac OS X ships with a native PDF viewer, it doesn’t do much beyond letting you view a file’s contents. Skim is both a top-notch PDF reader and markup tool designed just for the Mac. Use Skim to preview the internal links of a document, add notes, highlight text and more. You can even use Skim to create presentations and control them-right inside the app-using an Apple Remote. As more corporate documents are transmitted every day as PDF documents, this is one app you can’t do without.