Here is how this can be done...
<?php
include("mpdf.php");
ini_set('memory_limit','3000M');//extending php memory
$mpdf=new mPDF('win-1252','A4-L','','',15,10,16,10,10,10);//A4 size page in landscape orientation
$mpdf->SetHeader('Put your header here');
$mpdf->setFooter('{PAGENO}');
$mpdf->useOnlyCoreFonts = true; // false is default
//$mpdf->SetWatermarkText("any text");
//$mpdf->showWatermarkText = true;
//$mpdf->watermark_font = 'DejaVuSansCondensed';
//$mpdf->watermarkTextAlpha = 0.1;
$mpdf->SetDisplayMode('fullpage');
$mpdf->SetWatermarkImage('logo.png');
$mpdf->showWatermarkImage = true;
// Buffer the following html with PHP so we can store it to a variable later
ob_start();
?>
<?php include "yourphp.php";//The php page you want to convert to pdf
// asasas?>
<?php
$html = ob_get_contents();
ob_end_clean();
// send the captured HTML from the output buffer to the mPDF class for processing
$mpdf->WriteHTML($html);
//$mpdf->SetProtection(array(), 'mawiahl', 'password');//for password protecting your pdf
$mpdf->Output();
exit;
?>