For years I have owned my Mac and thought that because of its name, Preview was only able to open up PDF files and view pictures. After a bit of playing around I learned it can do much much more.
For starters, Preview is able to open most pictures formats and all PDFs. You can easily got to File > Export and then choose a different format to export it to. This will allow you to easily convert a picture into a PDF of vise versa.
You can easily annotate any document by going to Tools > Annotate. Highlighting, drawings symbols, and adding text is very simple to do. You can also highlight any area and crop it to create a new image files. Some other interesting tools are the Smart Lasso and Instant Alpha. These allow you to easily select only a portion of an image to erase or export.
Editing PDFs is where all your Windows 7 friends will be jealous of you. If you ever have the need to edit pages of a PDF document or combine them together it is very simple with preview. When you select the Thumbnail view you can easily see all the pages in the PDF on the left side. If there is a page you don’t want you can just select it and delete it. If you want to add more pages do the pdf just simply drag another PDF into the Thumbnail view and place it where you would like.
Many of these features are hidden in the options at the top. I sugest that you customize the toolbar to place your most important features front and center to you can easily get to them. You can always click on Help > Preview Help to find out more info.