Q: How do I change my operating system's default application for opening PDFs?

Answer

To set a PDF viewer as the default on Mac OS X:

1. Select any PDF file. Control-click to open the menu, and choose File > Get Info.
2. From the Open with: drop-down menu, select your preferred application, such as Adobe Reader or Preview.
3. Click Change All button, and in the subsequent dialog box, click Continue.

To set a PDF viewer as the default on Windows

• If no other PDF viewer is installed, once Adobe Reader is installed, it becomes the default.
• To set a preferred PDF viewer as the default:
  • Windows 7:
    1. Follow the menu path Start > Default Programs > Associate a file type or protocol with a specific program
    2. Highlight .pdf, then click Change.
    3. Choose your preferred PDF viewer, such as Adobe Reader.
  • In Windows XP
    1. Follow the menu path Start > Control Panel > Folder Options > File Types.

See also:

http://pcsupport.about.com/od/fixtheproblem/ht/defprogramxp.htm