Hello, my name is Marco and I am an Independent Advisor. I will do my best to help you.
If you have Android 9:
-Go to the settings option
-From the settings click on Apps & notifications
-From the Apps and Notifications section, click on Advanced option
-Now, click on the Default apps
- In the next window, you can see the list of available option, where you can change the default app selection.
-Click on the application, which you need to change the default app.
-Choose Adobe for your PDF files.