Starting with OS X 10.10 (Yosemite), Mac applications can include embedded app extensions. App extensions add custom functionality to your Mac. How you can use an app extension depends on what kind of extension it is.
At the time of this writing, there are four different kinds of app extensions available on the Mac:
–Action: Action extensions can manipulate content in another supporting app. Action extensions often work in text editing applications like Text Edit.
–Finder: Finder extensions add functionality to the Finder.
–Share Menu: Share extensions allow you to share content with other
–Today: These are widgets that can be added to the Today view in the Notification Center.
While there are several different kinds of app extensions available, every app extensions requires the user to enable them in System Preferences before they can be used. If you recently purchased an app and cannot figure out why you are unable to use a feature advertised in the app description, there is a chance that the feature you are looking for requires you to enable an app extension.
How to Enable an App Extension
To enable an app extension, open the System Preferences app on your Mac. In the System Preferences window, click on “Extensions.”
Once you are in the “Extensions” section of System Preferences, you will see a list of all the app extensions you have on your Mac. To enable or disable an app extension, simply check or uncheck the box next to each extension in the list. That’s all there is to it.