Only components designed in the "Sheet Metal" environment [or *.Par files converted to] can be saved as a DXF, using the flat pattern process,...but otherwise, you'd need to make a "Draft" file, orient a view for the face required, and save as DXF.
Make certain the view is placed at 1:1. >or< RMB on the scaled view, select "Draw In View", then save as DXF. [is sure way to be at model size]
Design Manager Streetscape Limited
Solid Edge ST9 [MP8] Classic [x2 seats]