Converts the selected object to a polygon, or a group of polygons. If the conversion creates a group of polygons (for example, when you convert a text object), then press F3 to enter the group before you can select an individual polygon.
Once you convert a line or a text object to a contour, you can no longer edit it as you normally would. Instead, you can edit the contour as you would any polygon, including using the Edit ? Points command to adjust its shape.