procedure TMainForm.AppMessage(var Msg: Tmsg; var Handled: Boolean);
const
  BufferLength: word = 255;
var
  DropPoint: TPoint;
  Counts : Integer;
  DroppedFilename: string;
  FileIndex: Word;
  pDroppedFilename: array[0..255] of Char;
begin
  if Msg.Message = WM_DROPFILES then
  begin
    DropPoint := Msg.pt;
      else if IsDropPointInside(DropPoint,ed) then
      begin
        Counts:=DragQueryFile(Msg.WParam, $FFFFFFFF, nil, 255);
        for FileIndex := 0 to (Counts - 1) do
        begin
          DragQueryFile(Msg.WParam, FileIndex, pDroppedFilename, BufferLength);
          DroppedFilename := StrPas(pDroppedFilename);
          ed.Text := DroppedFilename;
        end;
     end;
   DragFinish(Msg.WParam);
   Handled := true;
  end;
end;