How to Display or Hide File Extensions in Mac OS X Snow Leopard
Extensions are alien creatures to most Mac owners. However, Snow Leopard lets you see these three- or four-character add-ons at the end of a filename. The extension identifies which program "owns" a specific file, and therefore which application launches automatically when you double-click that file’s icon. Examples of common extensions (and the applications that own them) include
.pdf: Preview or Adobe Acrobat
.doc: Microsoft Word
.pages: Apple Pages
.key: Apple Keynote
.psd: Adobe Photoshop
.jpeg or .jpg: Preview or your image editor
.tiff or .tif: Preview or your image editor
.htm or .html: Your default Web browser
Why would someone want to see a file’s extension? It comes in handy when a number of different types of files are linked to the same application. For example, if you install Adobe Photoshop, both JPEG and TIFF images have virtually the same icon, so it’s sometimes very hard to tell one from the other. With extensions displayed, it’s easy to tell what type of file you’re looking at.
Follow this procedure to display extensions with your filenames:
Press Command+I (the letter between U and O on the keyboard) or choose File→Get Info.
The Info dialog opens.
Click the triangle next to the Name & Extension heading.
The Name & Extension section of the Info dialog expands.
Clear the Hide Extension check box to disable it.
The extension for the selected file is displayed
Close the Info dialog to save your changes.