How to flatten a 3D Curve object into 2D

Sorry if this is an obvious question.

I've isolated a curve out of a complex 3D geometry. I want to flatten this curve in 2D, allowing me to generate a 2D geometry that I can use to create something I later extrude back into 3D.

I have the design module, I do not (right now) have access to CAD support or software. Is this something I can do? Right now the best I can do is try and match the curve with a bezier polygon, which is slow and inaccurate.