KB10815 - Can the DK convert a line shape (a polygon outline) into a polygon shape?

Yes. This, can be done using the DK method TGIS_ShapeAsPolygon.

Other shape type conversions, such as point shapes to line shape, multi-point shape to single point shapes, etc., can be performed using similar DK methods, e.g., TGIS_ShapeAsLine, TGIS_ShapeAsPoint, etc.

Of course, first consider if the format of the layer accomodates mutiple shape types in the same layer. For example, it would be impossible to convert a line shape in a SHP layer into a polygon shape in the same layer, becuase SHP layers can hold only one shape type per layer.