procedure TForm49.FormCreate(Sender: TObject);
begin
  Caption := IntToStr(Handle);
end;

procedure SendCommandLine(const Wnd: HWND; const Msg: String);
var
  CDS: TCopyDataStruct;
  St: {$IFDEF UNICODE}String{$ELSE}WideString{$ENDIF};
begin
  St := Msg;
  CDS.cbData := (Length(St) + 1) shl 1;
  CDS.lpData := PWideChar(St);
  SendMessage(Wnd, WM_COPYDATA, 0, LParam(@CDS));
end;

procedure TForm49.Button1Click(Sender: TObject);
begin
  SendCommandLine(StrToInt(Edit1.Text), Edit2.Text);
end;

procedure TForm49.WMCopyData(var Msg: TWMCopyData);
var
  S: {$IFDEF UNICODE}String{$ELSE}WideString{$ENDIF};
begin
  // Есть хотя бы один символ и длина буфера чётна
  if (Msg.CopyDataStruct^.cbData <= 2) or ((Msg.CopyDataStruct^.cbData and 1) = 1) then
    S := ''
  else
  begin
    SetLength(S, (Msg.CopyDataStruct^.cbData shr 1) - 1);
    Move(Msg.CopyDataStruct.lpData^, Pointer(S)^, Msg.CopyDataStruct^.cbData);
  end;
  ShowMessage('Received string: "' + S + '"');
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Button1.Caption:= IntToHex(Handle,8);
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  CDS:TCopyDataStruct;
  St:string;

begin
  St:= 'ФЫВПОЛОЛДЖДЛЖЖ';
  CDS.cbData := Length(St) * SizeOf(Char);
  CDS.lpData := PChar(St);
  SendMessage(THandle($2D0562), WM_COPYDATA, 0, LParam(@CDS));
end;

procedure TForm1.WMCopyData(var Msg:TWMCopyData);
var
  FilenameForOpening: string;

begin
  SetLength(FilenameForOpening, Msg.CopyDataStruct.cbData div SizeOf(Char));
  Move(Msg.CopyDataStruct.lpData^, PChar(FilenameForOpening)^, Msg.CopyDataStruct.cbData);
  Label1.Caption:= FilenameForOpening;
end;