In OS X, all file types have a default application that opens when you double click on them. If you double click on a PDF file or a PNG file, chances are that your Mac will open it in Preview, Apple’s default PDF and image file app. If you’ve given an app like Adobe Reader, for example, permission to set itself as the default PDF app, then all PDFs will open in Reader.
Over time, you may have set apps as default that you no longer want to open your files. Conversely, you might want all JPG files to open in Preview, except one specific JPG file, which you’d like to open in Photoshop. Here’s how to make both of these situations work for you.
First up, to change the default app across all documents of a give file type, simply click on a file of that type, say, a PDF file. Then right-click on that file (or Control-click, if you like) and choose Get Info from the resulting contextual menu. Look toward the bottom of the Information window that will open up, and find the section that says “Open With:”
Click on the little triangle next to this section, or, if it’s already open, choose the app you’d like to set as that file type’s default from the pop up menu. Then, click on the Change All… button below that area, and from then on, all files of that type will attempt to open in the app you chose when you double click.
Now, if you’d like to open a specific file in a specific app, overriding the default app, simply right-click on the file, and then hit the Option key on your keyboard. The Open With contextual menu item will then change to “Always Open With,” and allow you to choose which Application you’d like to use to open this file with, all the time, no matter what the default app is set to.
Via: OS X Daily