Hi @Anonymous
On the Modify ribbon tab > expand the Design panel > you should see the Convert 2D to 3D Polyline command. once the polyline is converted, select it and modify each vertex elevation from the AutoCAD Properties palette!
![capture.png capture.png](https://forums.autodesk.com/t5/image/serverpage/image-id/902343iFBF9BC908E1A0B41/image-size/large?v=v2&px=999)
![capture2.png capture2.png](https://forums.autodesk.com/t5/image/serverpage/image-id/902346iDD05DC67BF42B3CB/image-size/large?v=v2&px=999)
With that said, it is recommended to use Civil 3D Feature Lines! they are much easier to work with and user friendly when setting the vertex elevations along, also they can contain arcs where as curved segments will be tessellated lines on a 3D Polylines!
Hope this helps,
Samir Rezk
Technical Support Specialist