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procedure TForm1.WebBrowser1DocumentComplete(Sender: TObject;
  const pDisp: IDispatch; var URL: OleVariant);
begin
playsound('c:\ding.wav', 0, SND_FILENAME or SND_ASYNC);
repeat;
Application.ProcessMessages;
until WebBrowser1.ReadyState = READYSTATE_COMPLETE;

begin
  if (WebBrowser1.LocationURL='http://beispiel.abc/formular.php') then
   begin
    WebBrowser1.OleObject.document.forms.item(0).elements.item('yourmessage').value:='TEST';
    WebBrowser1.OleObject.document.forms.item(0).submit;  // Daten an Server senden
   end;
end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
// Application.ShowMainForm:=False;
 Webbrowser1.Navigate('http://beispiel.abc/formular.php');
end;