functions.php

<?php 
// See: https://snippets.webaware.com.au/snippets/filter-documents-in-wordpress-media-library/

/**
* add custom "mime types" (file supertypes)
* @param array $post_mime_types
* @return array
*/
function filterPostMimeTypes($post_mime_types) {
    $post_mime_types['application'] = array('Document', 'Manage Documents', _n_noop('Document <span class="count">(%s)</span>', 'Documents <span class="count">(%s)</span>'));
    return $post_mime_types;
}
add_filter('post_mime_types', 'filterPostMimeTypes');