hstr is HSTR for the source file if this message is sent by DrgDragFiles, and is HSTR for the target file if this message is sent by DrgAcceptDroppedFiles.

This message is sent by DrgDragFiles to its caller when the move or copy operation is completed, regardless of success or failure. It is also sent by DrgAcceptDroppedFiles when a file has been successfully dropped on the caller.