Geospatial Location Tool "Mark Location" is grayed out

I just downloaded a 30-day trial of Adobe Acrobat Pro DC specifically to evaluate the geospatial registering functionality described here:

Geospatial PDFs, Adobe Acrobat

However, when I right click on the map, the "Mark Location" menu item in the contextual menu is grayed out. It is not clear how to create the geospatial PDF by "Georegistering a PDF map or scan of geospatial data" as this is not documented on that help page.

Can someone explain how to add georegistration to a PDF map?

Thanks.