Set Option UTF-8 not responding

[Parviz Khorrami]

Good day,
I have a web page which I need to create a PDF. I'm new to Snappy, so everything works well and the PDF gets generated but the posted values from DB is not showing correctly since the characters are in Persian, I appreciate any help.
Thanks

pdftest.php file:

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

use Knp\Snappy\Pdf;
$billno = $_POST["billno"];
$custname = $_POST["custname"];
$balance = $_POST["balance"];
$address = $_POST["address"];
$phone = $_POST["phone"];
$merchname = $_POST["merchname"];
$merchqty = $_POST["merchqty"];
$merchdetails = $_POST["merchdetails"];
$snappy = new Pdf('C://"Program Files/"/wkhtmltopdf/bin/wkhtmltopdf.exe');
header('Content-Type: application/pdf');
$snappy->setOption('page-size', 'A5');
$snappy->setOption('no-background',false);
$snappy->setOption('margin-top', '1');
$snappy->setOption('margin-bottom', '0');
$snappy->setOption('margin-left', '0');
$snappy->setOption('margin-right', '0');
$snappy->setOption('encoding', 'UTF-8');
$snappy->setOption('post', array('billno' => $billno,
                                 'custname' => $custname,
                                 'balance' => $balance,
                                 'address' => $address,
                                 'phone' => $phone,
                                 'merchname' => $merchname,
                                 'merchqty' => $merchqty,
                                 'merchdetails' => $merchdetails
                                ));
echo $snappy->getOutput('http://www.bnfgallery.ir/pdf.php');

The output pdf file image:

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