On Windows powered computers, we use a specific software to open a file by default. You can do the same thing on Android powered smartphones if you want. Therefore, when you go to open a file, a window like the image will appear. Check the " Use by default for this action" option below , it will be set as default. If you do not want to use it as default then go to Settings , from there select the Apps option. Then you will see the list of apps , select the app from there and click on Clear defaults , the default mode will be off.