Click the Features | Change Type | Change Type | Polygon to Polyline command or right-click on a polygon and click Polygon to Polyline to convert one or more selected polygons into polylines. Each selected polygon is converted to a new separate polyline.
The new polyline retains the line properties from the polygon. If the object name has not been changed from the default Polygon, the object is renamed Polyline. If the object name had been altered, the custom object name is retained.
If objects should be edited in a base map, click on the object in the Base layer to select it. Click the Features | Group | Start Editing command to enter editing mode. Then, click the Features | Change Type | Change Type | Polygon to Polyline command. The polygon is changed to a polyline. Click the Features | Group | Stop Editing to end object editing mode in the base map.
Polyline to Polygon