Wordpress Media Bank - Filter by Mime Type

functions.php

function modify_post_mime_types($post_mime_types) {
    $post_mime_types['application/pdf'] = array(__('PDF'), __('Manage PDF'), _n_noop('pdf <span class="count">(%s)</span>', 'pdfs <span class="count">(%s)</span>'));
    $post_mime_types['application/msword'] = array(__('Word doc file'), __('Manage Doc'), _n_noop('word doc <span class="count">(%s)</span>', 'word docs <span class="count">(%s)</span>'));
   return $post_mime_types;
    $post_mime_types['application/rtf'] = array(__('Rich text file'), __('Manage RTF'), _n_noop('rtf <span class="count">(%s)</span>', 'rtfs <span class="count">(%s)</span>'));
   return $post_mime_types;
}
add_filter('post_mime_types', 'modify_post_mime_types');