function pdfscreen(){
  links=screen.width/2-300;
  oben=screen.height/2-400;
  window.open("","pw_window","width=600,height=400,top= " + oben + ",left= " + links + ",toolbar=0,location=0,directories=0,status=0,menubar=0, scrollbars=yes,resizable=1,copyhistory=0");
}