if( isset($this->data['file']) ) {

  $allowed_types = array('image/png', 'image/jpg', 'application/pdf', 'application/vnd.openxmlformats-officedocument.wordprocessingml.document', 'xls', 'application/msword', 'application/vnd.ms-excel', 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet' );

  if ( in_array($this->data['file']['type'], $allowed_types) ) {

    //move temp file
    $upload_dir = wp_upload_dir();
    $upload_dir = $upload_dir['path'];

    $tmp_name = $this->data['file']['tmp_name'];
    $name     = $this->data['file']['name'];
    move_uploaded_file( $tmp_name, "$upload_dir/$name" );
    $file = "$upload_dir/$name";

    //get file url
    $content_url = untrailingslashit( dirname( dirname( get_stylesheet_directory_uri() ) ) );
    $content_dir = untrailingslashit( WP_CONTENT_DIR );
    $file        = wp_normalize_path( $file );
    $content_dir = wp_normalize_path( $content_dir );
    $url         = str_replace( $content_dir, $content_url, $file );

    $attachments = array( 'file' => $file, 'url' => $url, 'name' => $name );

    $this->data['attachments'] = $attachments;
  }
  unset($this->data['file']);
}