Mac101: Always Open With
A file icon's stylized display often shows you a relationship between the file and the application that it opens in. For example, an HTML file that stores web page information might display a small Safari compass or a Firefox globe. Word files are marked with a blue W, Powerpoint files with a P, QuickTime movies with a stylized Q. These icon hints indicate which program will open and attempt to read the file when you double-click it in Finder.
Many file types can be used in more than one program. For example, you can play MP3 files in QuickTime or in iTunes, you can open a text file in TextEdit or in Word, movies in QuickTime or VLC. Finder allows you to change the application associated with each file. Here's how: Control-click (right-click) any file. A contextual menu opens over the file. Release any keys you are pressing and then press the option key. The menu item that had said "Open With" changes to "Always Open With". Select any application from the Always Open With submenu. Two things happen. First, your file will open in the application you select. Second, Finder updates the file's association so it will always open in that application. Its icon updates, changing to reflect its new "native" application.
Say, however, you want all your MP3 files to open in QuickTime or all your text files to open in TextEdit, or so forth. Do this instead. Select any representative file in Finder and choose File -> Get Info (Command-I). Locate the section of the Info pane named "Open with". Select the Application you want to use from the pop-up menu and then click Change All... By doing this, you instruct OS X to change the application association for all files on your computer that share the same type, text, MP3, MOV, XLS, or whatever.
