Generate PDF by Ajax

Question

What I am trying to do is for the user to click the button generate of a form, manages a .pdf by Ajax request, ie I have three pages, where the Index.php this form, the controller.php this is the ajax script where to send the data to generate the .pdf on the page procTermo.php. I do not know if this is possible or I am doing something wrong. Note: To generate the PDF use the DOMPDF.

index php.

<form id="termo1" action="controller.php" method="POST" target="_blank">
                    <div class="panel-body">
                        <div class="form-group">
                            <label class="col-xs-3 control-label">Serial:</label>
                            <div class="col-xs-3">
                                <input type="text" class="form-control" name="serialTermo1" required/>
                            </div>
                        </div>
                        <div class="form-group">
                            <label class="col-xs-3 control-label">Objeto:</label>
                            <div class="col-xs-6">
                                <textarea class="form-control" rows="5" name="objTermo1"></textarea>
                            </div>
                        </div>
                        <div class="cleanfix"></div>
                        <center><button class="btn btn-default" name="btnGerar" value="gerar1">Gerar <span class="glyphicon glyphicon-save"></span></button></center>
                    </div>

php controller.

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>
<script type="text/javascript">
    var data_to_send = JSON.parse('<?php echo json_encode($_POST);?>');
    $.ajax({
        type: 'POST',
        url: 'procTermo.php', 
        data: data_to_send,
        success: function(data){alert(data);},
        failure: function(errMsg) {
        alert(errMsg);
    }       
}); 
</script>

procTermo.php

switch ($_POST['btnGerar']) {
case 'gerar1':
$content = "
<div id='title'><u><b>Capa Termo</b></u></div></center>
<div id='content'><p><b>Serial</b>: ".$_POST['serialTermo1']."</p><p>
<p><b>OBJETO</b>: ".$_POST['$objTermo1']."</p></div></body></html>
";
    $dompdf->load_html($content);
    $dompdf->render();
    $dompdf->stream("saida-termo1.pdf",array("Attachment" => false));
    break;