Summary
CP_CH2D3D: Converts all the selected 2D Polylines to 3D polylines. A 3D polyline can hold different Z values in each of its vertex. The new 3D polylines thus formed will look exactly like the 2D polylines except that internally they are 3D and therefore can hold Z values.
CADPower -> Polyline Tools -> Change 2d->3d->2d -> 2D-to-3D
The standard object selection dialog appears and allows polylines and lines to be selected. Click Apply and all the 2D polylines are converted into 3D polylines. The original 2D polyline will be erased.
Tech Info: CP_CH2D3D changes the DXF Group Code 70 of each polyline, adds the 8 bit and recreates a 3D polyline. The 3D polyline thus created has the 3D flag set. The 3D polyline acquires new handles but any extended entity data in the 2D polyline will be transferred to the 3D polyline.