However, you may not see the dialog box that asks for permission. They’re not supposed to change the default Mac app for a file type without the user’s agreement. The installation procedure of some apps will change the default.

These and other file types open in a default program set by the operating system. Maybe you want all JPG picture files to open in a photo editor instead of OS X Preview. Why would you want to change a default Mac app for a file type? Let’s say you want to open a video file using VLC Media player instead of Apple’s QuickTime Player. Why Change Default Mac App for a File Type Changing the Default Mac app is a simple procedure that will save users some time and avoid annoyances.

We’ll show users how to take control of what apps open when they double-click a certain file type. However, if a user downloads and installs Adobe’s Acrobat Reader or Adobe Acrobat DC, the default file type will change so that all PDF files will open with Adobe Acrobat. For example, PDF files open by default in the Mac Preview app. Any time a user installs a new application on a Mac, it becomes the default Mac app for that file type.