Some documents you have can be opened by more than one application on your computer. For example, PDFs can be opened in the Adobe Reader and Preview. RTF documents can be opened by Text Edit and Word. JPEGs can be opened in Preview, Safari and Photoshop.

However, when you double click the document it typically opens in the default app for that type of document.

If you want to open a document in a different app this one time, simply drag the document and drop it on top of the application you want to open it in on the Dock. Make sure the application highlights first before you let go.

Also, a right click (or ctrl+click) on the document will pop up a menu. Select 'open with' then there will be a menu of programs that can open that document.

Can also do a "Cmd-I" Get Info, then select an application in the "Open with" popup. If the application you desire isn't listed, select "Other" to go to a different application on your drive. (The unlisted app you choose may or may not work with the file, depending on type.)

This is helpful if a file defaults to the version of an app in which it was created and which is still on your drive.(for example, PSElements v.1, OS9) If you want it to default to a newer version (for example, PSElements 3 - OSX) without opening the newer app & fishing around on your drive for the file.