You can create one or more curves in a sketch by projecting an edge, loop, face, curve, or external sketch contour, set of edges, or set of sketch curves onto the sketch plane.
To convert an entity:
In an open sketch, click a model edge, loop, face, curve, external sketch contour, set of edges, or set of curves.
Click Convert Entities
on the Sketch toolbar, or click Tools,
Sketch Tools,
Convert Entities.
The following relations are created:
On Edge. Created between the new sketch curve and the entity, which causes the curve to update if the entity changes.
Fixed. Created internally on the endpoints of the sketch entity so the sketch remains in a "fully defined" state. This internal relation is not displayed when you use Display/Delete Relations. Remove the Fixed relation by dragging the endpoints.