The Creates Lines from Areas tool will create a new line features using the same vertices as the selected areas.
With an area feature selected with the Digitizer,
choose this option from the Digitizer toolbar or select from the Digitizer menu or
right-click context menu under Create Line Features or Advanced Feature Creation.
This option can also be accessed in 3D View from Advanced Feature Creation section of context menu when the Digitizer Mode is active.
The Create Line Feature(s) from Selected Area Feature(s) option will add a new line feature(s) to a new or existing layer of data consisting of the same vertices of the selected area feature(s), using the Modify Feature Info dialog.