Change Default PDF Viewer

Change to the Acrobat PDF viewer in Windows:

1. Right-click on the thumbnail of any PDF file.
2. On the menu, click Properties.
3. A new dialog box will appear. In the first subsection, the text “Opens with:” indicates which PDF viewer is set as your default. Click the Change button.
4. Select Adobe Acrobat DC or Reader from the list as your default.
5. Click OK to save and apply changes.

Change to the Acrobat PDF viewer in Mac OS:

1. Right-click on the thumbnail of any PDF file.
2. On the menu, click Get Info.
3. Navigate to the Open With: section and select Adobe Acrobat DC or Reader from the drop-down list.
4. Tap Change All to apply this change to all future PDF documents. Tap Continue to finish.

Source: Adobe