Civil 3D can definitely use LAS files, so I'm not sure why they told you that. Is this a traditional ground elevation Lidar survey, or is it a ground-based point cloud (like a scan of a 3D object)?
For terrain elevations, in Civil 3D if you go to Create Ground Data, Create Point Cloud, LAS is one of the many options available to pick from. For point clouds of solid objects (like a scan of a bridge), they'll want to use this tool: apps.exchange.autodesk.com/ACD/en/Detail/Index?id=appstore.exchange.autodesk.com%3apointcloudfeatureextraction%3aen
You can convert LAS to multipoint in GIS and from there to a text file, but better to just use LAS in Civil 3D. They can also create surfaces from shapefiles or survey files/contours on your SDE server. Civil 3D is very GIS data friendly. It sounds like these are folks who are used to the older AutoCAD that doesn't support all this functionality.