$('.form_calc .btn_wrap .btn-download').click(function(){
        //Скачать предложение
        var path = '/pdf/pdf.php';
        var formData = $("#form").serialize();
        formData += "&action=download";
        var success = function( response ){
            if (response.status == "OK") {

                /*if (typeof (window.open) == "function") {
                    window.open(response.message);
                }
                else {
                    window.location.href = response.message;
                }*/
                //alert (response.message;);
                window.location.href = response.message;
            }
            else {
                alert (response.message);
            }
        }
        $.post(path, formData, success, "json");

        return false;

    });

<?php

require_once('../dompdf/autoload.inc.php');

use DompdfDompdf;

// instantiate and use the dompdf class
$dompdf = new Dompdf();
$html = '../index1.html';
$content = file_get_contents($html);
$dompdf->loadHtml($content);

// (Optional) Setup the paper size and orientation
$dompdf->setPaper('A4', 'landscape');

// Render the HTML as PDF
$dompdf->render();

// Output the generated PDF to Browser
$dompdf->stream();

?>