AutoCad 3D :: Extract 2D Elements Used To Create 3D Model

I've recently been given a *.dwg file that seems to contain a 3D model composed of blocks. I'm a long-time SolidWorks user, and in my parlance, what I've got is an assembly composed of individual parts.

I need to create a 2D version of each 3D part. Currently, my process isCut & paste 3D component into new document.

Select all and perform 'flatten,' removing hidden lines.
Select all and explode.

Manually remove a zillion duplicate and unnecessary line segments. Manually fix radiused / filleted corners, which have become a bunch of little straight line segments. Draw a polyline around the whole part. Run 'boundary' to create a new polyline approximating the original shape.

Clearly, this is not very efficient - nor does it produce an exact 2D duplicate of the face of the 3D part; what I get is a close approximation. I don't use AutoCAD to do 3D work, but I assume that, much like SolidWorks, a 2D sketch is created first and then extruded into the 3D objects.

This, in turn, leads me to believe that there ought to be a way to extract that 2D sketch intact for use elsewhere. How should I go about doing this?