When the default application isn’t the one you want to use.
In Mac OS, each document is automatically associated with an application. Double-clicking the document icon in the Finder automatically opens the document in the default application.
But you don’t have to choose that application to get the job done. You can choose from a menu of installed applications that may be able to open the file.
- Select the icon for the document you want to open.
- Choose File > Open With to display a submenu menu of applications.
Control-click (or right-click) on the selected icon and choose Open with from the contextual menu that appears to display a submenu of applications.
- Choose the application you want.
Why would you do this? Well suppose you have an image file that would normally open in Preview, but you want to do some heavy-duty editing on it in Photoshop. While you could always drag the document icon onto the Photoshop icon to open the document in Photoshop, this makes it possible to open the document in Photoshop without displaying the Photoshop icon.
You can learn more documents and applications in Chapter 10: Application Basics in Mac OS X 10.5 Leopard: Visual QuickStart Guide.