Form with file upload not working inside HTML Modal

This is my code

<div id="myModal" class="modal fade" role="dialog" aria-hidden="true" data-backdrop="static" data-keyboard="false">
     <div class="modal-dialog">
                <!-- Modal content-->
           <div class="modal-content">
                <div class="modal-header">
                       <h4 class="modal-title" id="jobTitle"></h4>
                <form action="<?=$_SERVER['PHP_SELF']?>" method="post" id="editJobVacancyForm" role="form" data-toggle="validator" enctype="multipart/form-data">
                      <div class="modal-body">
                        <div class="form-group">
                            <div class="row">
                                <div class="col-xs-5">
                                    <label for="addJobAdvertisement" class="control-label">Upload Advertisement:</label>
                                <div class="col-xs-7">
                                    <input type="file" name="addJobAdvertisement" id="addJobAdvertisement" placeholder="Upload your advertisement">
                                    <input type="checkbox" id="removeAdvertisement" name="removeAdvertisement" value="removeAdvertisement"> Remove Advertisement
                     <div class="modal-footer">
                          <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
                          <button type="submit" name="edit" class="btn btn-default">Update</button>

Following code always gives TRUE with/without a file.


I did a same form without a HTML Modal. It works fine. But this code didn't pass the uploaded file.

Other input with in this form with in Modal are passed correctly (I removed them, because form is very long).