$pdf = pdf_new( );
pdf_open_file($pdf, "/path/to/your.pdf");
pdf_begin_page($pdf, 600, 800);
$testimage = pdf_open_image_file($pdf, "jpeg", "myimage.jpg");
pdf_place_image($pdf, $testimage, 0, 0, 0.5);
pdf_end_page($pdf);
pdf_close($pdf);
pdf_delete($pdf);