How to open a GPX / CSV / KML / KMZ / GeoJSON / PDF file in Maps Pro?
First one is the easiest, just right-click the file > Open with > Maps Pro.
Second one is by opening Maps Pro, open the Menu (via the arrow in the lower-right corner) > Overlays > Add GPX / CSV / KML / KMZ / GeoJSON files ... > Click the corresponding format in the list > Browse to the file you want to open > Open
Then you can manage your overlays (add/remove them) via the Overlay menu.