The default Mac application for opening and printing PDF files is Preview. If you’d like to change the default to another application, all you have to do is:

  1. Select any PDF document and do a File > Get Info in the Mac’s Finder.
  2. Pick the new application in the “Open with:” pop-up menu.
  3. Finally, click the Change All… button.

That’s it. Now all your PDF documents will open automatically with the new application when you double-click on them in the Finder.