Create pdf using the R&OS

[dane]

who have used the r&os module for creating pdf?? i cant create a simple hello world bcoz i always get this message == file does not begin with '%PDF-'

here is my code:

// make a new pdf object
$pdf = new Cpdf();
// select the font
$pdf->selectFont('./fonts/Helvetica');
$pdf->addText(30,400,30,'Hello World');
$pdf->stream();