How can I export curves(nurbs) to AutoCAD without converting to mesh? I have some curves (nurbs) in blender and I want to use them in AutoCAD the same way as same curves. However, when I export the file as .fbx or .dxf and open in AutoCAD, the curves are converted to meshes.

How can I preserve the state of these when exporting? Is it possible?
The OBJ exporter supports import/export nurbs curves natively.
Otherwise you could find a list of all formats autocad supports, then see if there is support within blender for any of these formats (as 3rd party addons for eg, perhaps shapefile for example).