uses ComObj;
   .....

procedure TForm1.Button1Click(Sender: TObject);
var
  NVstamp : Variant;
  indx : Integer;
  retVal : Integer;
begin
  NVstamp := CreateOLEObject('PDFstamp.Neevia');

  indx := NVstamp.CreateNewStamp;
  NVstamp.Stamps[indx].StampType := 0;
  NVStamp.Stamps[indx].Name := 'Stamp1';
  NVStamp.Stamps[indx].Text := 'WATERMARK';
  NVStamp.Stamps[indx].FontName := 'Arial';
  NVStamp.Stamps[indx].TextRenderingMode := 0;
  NVStamp.Stamps[indx].TextColor := '#FF0000';
  NVStamp.Stamps[indx].X := 'center';
  NVStamp.Stamps[indx].Y := 'center';
  NVStamp.Stamps[indx].PlaceAs := 0;

  retVal := NVStamp.StampPDF('c:\in.pdf', 'c:\out.pdf');

  if retVal <> 0 then
    Application.MessageBox(PChar('Error code=' + IntToStr(retVal)),'',0)
  else
    Application.MessageBox('Done','',0);

end;