On WF 4 the draw_symbol_palette.drw is located in C:\proe_intgr\proent\symbols\palette. Navigate to this folder and call up the draw_symbol_palette.drw and add whatever symbol you want and then save the drawing.
As stated above, you need to open the draw_symbol_palette.drw file, however the path stated above is only valid for the poster. Do a search within windows for the above named file, it will be in the /symbols directory.