i have the following code
<?php
require_once 'includes/initialize.php';
set_include_path( get_include_path() . PATH_SEPARATOR . CHARTS_PATH);
require_once "class/pDraw.class.php";
require_once "class/pImage.class.php";
require_once "class/pData.class.php";
// create data set
$myDataset = array(0, 1, 1, 2, 3, 5, 8, 13);
$myData = new pData();
$myData->addPoints( $myDataset );
$myData->setAxisName( 0, "Numbers" );
// define image object
$myImage = new pImage( 600, 300, $myData );
$myImage->setFontProperties( array( "FontName" => CHARTS_PATH . "/fonts/GeosansLight.ttf", "FontSize" => 15 ) );
$myImage->setGraphArea( 25,25, 475,275 );
$myImage->drawScale();
// output bar chart
$myImage->drawBarChart();
header( "Content-Type: image/png" );
$myImage->Render( null );
?>
how can i modify the code so that it produces pdf document instead of image files