adds_field_to_contact.liquid

<script> 
  $(document).ready(function(){
    $('<div class="form-group"><div style="margin-top: 16px;" id="contactpage_custom" class="field"><label for="contactpage_custom" class="control-label">Empresa</label><br><input type="text" name="contact[custom]" id="contact_pcustom" class="text form-control"></div></div>').insertAfter("#contactpage_name")
  });
  $("#contact_form").submit(function(){
    $("#contact_message").val("Empresa: "+ $("#contact_pcustom").val() + "\n" + $("#contact_message").val())
  });
</script>