You may receive an ESRI Shapefile collection from a GIS user for a data source in generating a surface. This is typically a ShapeFile Type 1 (Point) or Type 2 (Polyline) which contains the XY values in the .SHP file, along with the elevations in a field of the associated .DBF file.
The list of file formats that CAD users need to deal with never seems to stop growing. For a long time the ESRI Shapefile was pretty much the exclusive format from ESRI users but it was always an export from the GIS. Now users find themselves receiving folders of content with the folder having a .GDB (GeoDatabase) extension.