AutoCAD Map and AutoCAD Civil 3D has the ability of storing Coordinate Reference System embedded in a drawing.
I have been making some testing and I think that this is stored in the NOD (Named Object Dictionary) because I found a entry named "Autodesk_MAP".
Inside this entry I only found some objects identifiers, proxy objects, RXClass objects and this kind of stuff.

There is a way or read and write Coordinate Reference System using .NET API a vanilla Autocad edition, not Map or Civil 3D?