Open Acrobat and then open the "Preferences for Acrobat ("Edit => Preferences", and on the general tab uncheck the option for "Tell me if Acrobat is not my default PDF viewer", and close Acrobat. Open Reader and then open the "Preferences", "Edit => Preferences", on the General tab check the "Tell me if Acrobat Reader is not my default PDF viewer". Now use Windows explorer to find any PDF, right mouse click on the PDF icon and select the "Open with" menu item and them select "Adobe Reader" .