Upload upload files with Jquery and Modal Bootstrap validation

Colleagues.

I have a website where the form is validated with Jquery through a modal Bootstrap and everything is OK the message is sent. But we've included a file field for file uploads. The problem we're encountering is that the file does not go to the submit validation page:

<form role="form" class="contact-form" id="contact-form" method="post" enctype="multipart/form-data">
<div id="final" class="form-group invisivel radio">
 <div class="form-group">
    <label for="Arquivo">Arquivo:</label>
    <div class="input-group margin-bottom-sm">
      <span class="input-group-addon"><i class="fa fa-upload fa-fw" aria-hidden="true"></i></span>
      <input name="Arquivo" class="form-control" type="file" placeholder="Envie arquivo">
    </div>
    <small id="emailHelp" class="form-text text-muted">Arquivos suportados: PDF, .doc e .docx</small>
 </div>     
</div>  

JQUery

<script> 
           $('form').submit(function () { 
function (d) { 
               $.post("enviar.php", $(".contact-form").serialize(), function(d) {
                    $('#success').html(d);
                    $('#myModal').find(".modal-body").html(d); 
                    $('#myModal').modal('show'); 
                }); 
               return false; 
           }); 
          </script>

PHP

echo $_FILES['Arquivo']['name'];

How would I do by leveraging the jquery code for validation with Modal Bootstrap?