"Proceed as if you were going to open the document using the contextual menu, but don’t select Open With just yet. Instead, press and hold the Option key down. Just as with the top-level menus, holding down the Option key reveals choices that aren’t normally visible. In this case, Open With changes to read Always Open With. So that’s it—select Always Open With, scroll down to find the application you’d like to use, and release the mouse. Bingo! You’ve now set the Always Open With application for the selected document (or documents, if you highlight more than one)."