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 or mention this post in your own blog if this helped you. Enjoy!