A Shapefile that was "mapexported" from autocad civil 3d 2019 wont allow me to add fields to the Attribute table. It will allow me to click add field, but when the field menu pops up, no new field has been added, and the "Add Field" button at the top of the screen has been grayed out. Is there any way to add new fields to this shape file? I need to create new fields and add text into the attribute table.