Windows 10

1. Open the Start Menu 

2. Click on Settings

3. Go to Apps

4. Go to Default apps

5.  Scroll down

6. Select one of the methods below:

    Method 1: Choose default apps by file type

    Method 2: Set defaults by app

Method 1: Choose default apps by file type 

7. Click on Choose default apps by file type

8. Scroll down to the Name .pdf

9. Choose your desired default app

10. Close all appropriate windows

Method 2: Set defaults by app

8. Click on Set defaults by app

 9. Choose desired program to default

10. Click Set this program as default 

11. Click OK

12. Close all appropriate windows