Answered getContents

     * Get the contents of the file
     *
     * @return string The contents of the file
     */
    public function getContents() {
        return @file_get_contents($this->path);
    }

$file = MODX_BASE_PATH . 'path/to/file';
if (file_exists($file)) {
   $content = file_get_contents($file);
}