If you are an OS X user, and you find files of a certain type, say PDFs, are opening in one applications but you want them to open in a different one, you can easily change the association using Finder.
How to Re-associate File Types with Applications in OS X
- Select a file in Finder and ctrl-click it.
- Select "get info" from the context menu.
- Find the "open with" section in the "get info" menu that appears.
- Select your desired application from the drop down list.
- Click "change all" to set the association between that file type and the application you selected.
This has worked in OS X Tiger, Leopard and Snow Leopard. You can use this method to, say, open all PDFs in the native OS X "Preview", Adobe's Acrobat, or Skim, for instance. Please leave a comment if this helped you. Enjoy!