The file types that you have specified 'application/msword', 'application/vnd.ms-excel', 'application/pdf' are already supported by media uploader.

To see the default supported mime file types, call [wp_get_mime_types()][2] function.

Use [upload_mimes][1] filter as shown in following code  to make media uploader to accept files types other than the default.

Add following code in your themes functions.php file

    // Add the filter
    add_filter('upload_mimes', 'custom_upload_mimes');

    function custom_upload_mimes ( $existing_mimes=array() ) {

    // Add file extension 'extension' with mime type 'mime/type'
    $existing_mimes['prc'] = 'application/x-mobipocket'; 

    // and return the new full result
    return $existing_mimes; 
    }


  [1]: http://codex.wordpress.org/Plugin_API/Filter_Reference/upload_mimes
  [2]: http://codex.wordpress.org/Function_Reference/wp_get_mime_types