pdf merge and stamp

<?php 
require 'vendor/autoload.php';

$writer = new SetaPDF_Core_Writer_Http('output.pdf', true);
$document = SetaPDF_Core_Document::loadByFilename('test.pdf', $writer);

$formFiller = new SetaPDF_FormFiller($document);
$fields = $formFiller->getFields();

$stamper = new SetaPDF_Stamper($document);


// Get Post Data 
$name = $_POST["name"];
$email = $_POST["email"];

$signature = $_POST["base64"];
$signature = base64_decode(preg_replace('#^data:image/\w+;base64,#i', '', $signature));


// Set fields
$fields['NAME']->setValue($name); // add some randomness
$fields['EMAIL']->setValue($email);


// Stamp Image
$image = SetaPDF_Core_Image::getByPath('signature.png');
$imageStamp = new SetaPDF_Stamper_Stamp_Image($image);
$stamp = new SetaPDF_Stamper_Stamp_Image($image);

// Set Signature
$stamper->addStamp($stamp, array(
    'position' => SetaPDF_Stamper::POSITION_LEFT_BOTTOM,
    'translateX' => 0,
    'translateY' => 10,
));
$stamper->stamp();

$document->save()->finish();