public function getPaperSize($paperSize = null)
    {
        $size = $paperSize !== null ? $paperSize : $this->paperSize;
        if (is_array($size)) {
            return $size;
        } else if (isset(Adapter\CPDF::$PAPER_SIZES[mb_strtolower($size)])) {
            return Adapter\CPDF::$PAPER_SIZES[mb_strtolower($size)];
        } else {
            return Adapter\CPDF::$PAPER_SIZES["letter"];
        }
    }