If I read your question correctly (at least literally) you want to unfold a SKETCH? No, No, No. Unfolding is only (logically) possible on an actual 3D model.
So ctopher is correct - you need to make some sheet metal from the imported 2D DXF/sketch first. THEN you can unfold it.
3/4 of all the Spam produced goes to Hawaii - shame that's not true of SPAM also.......