Like many things in Civil3D, they can be done but how it’s done isn’t so obvious. In the process of adding a DEM surface to your drawing you may notice that you can’t project it to another coordinate system (that of the drawing). Here is a step-by-step procedure including assigning a coordinate system to the current drawing.
A Civil3D forum user recently stated they have “been supplied ~500 .tiff files from a DEM which contain elevation data” and the prospect of repeating the built in Create Surface from DEM tool 500 times did not appeal to them (only to have 500 separate surfaces). So we set out to create a tool to help.