public function getContentStream()
    {
        $dict = $this->getPageDictionary();
        $contents = PdfType::resolve(PdfDictionary::get($dict, 'Contents'), $this->parser);
        if ($contents instanceof PdfNull) {
            return '';
        }

        if ($contents instanceof PdfArray) {
            $result = [];
            foreach ($contents->value as $content) {
                $content = PdfType::resolve($content, $this->parser);
                if (!($content instanceof PdfStream)) {
                    continue;
                }
                $result[] = $content->getUnfilteredStream();
            }

            return \implode("\n", $result);
        }

        if ($contents instanceof PdfStream) {
            return $contents->getUnfilteredStream();
        }

        throw new PdfReaderException(
            'Array or stream expected.',
            PdfReaderException::UNEXPECTED_DATA_TYPE
        );
    }