Create a curve from a surface edge, isoparm, or curve-on-surface

To create a new curve from a surface component curve

Select an edge, isoparm, or curve-on-surface.
Select Curves > Duplicate Surface Curves.
When construction history is on, the curve remains linked to the original surface. Transformation is relative to the original surface, and changes to the component curve from which it was created change the duplicated curve.

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