creo4 config.pro option documentation for: INTF2D_IN_ACAD_APPEND_BY_DND 
intf2d_in_acad_append_by_dnd
yes
, no
*
Allows you to append a DXF or DWG drawing by dragging it to an existing Creo drawing.
yes
- Allows you to drag and append DXF or DWG drawings from your local directory to an existing drawing.
no
- Creates a new drawing when you drag drawings from your local directory to an existing drawing.