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//Add Extra Media Type Filters to the WordPress Media Manager

    function modify_post_mime_types( $post_mime_types ) {  
      
        // select the mime type, here: 'application/pdf'  
        // then we define an array with the label values  
      
        $post_mime_types['application/pdf'] = array( __( 'PDFs' ), __( 'Manage PDFs' ), _n_noop( 'PDF (%s)', 'PDFs (%s)' ) );  
      
        // then we return the $post_mime_types variable  
        return $post_mime_types;  
      
    }  
      
    // Add Filter Hook  
    add_filter( 'post_mime_types', 'modify_post_mime_types' );