DocumentController.php

    public static function getPdfCertificate(array $args)
    {
        ValidatorModel::notEmpty($args, ['path', 'documentId']);
        ValidatorModel::intVal($args, ['documentId']);
        ValidatorModel::stringType($args, ['path']);

        $path = $args['path'];
        $documentId = $args['documentId'];

        $tmpPath = CoreConfigModel::getTmpPath();

        $signaturePath = $tmpPath . 'signature_' . $documentId . '.pkcs7';
        $signatureInfoPath = $tmpPath . 'signatureInfo_' . $documentId . '.txt';

        if (file_exists($signatureInfoPath)) {
            $content = file_get_contents($signatureInfoPath);
            if ($content !== false) {
                return $content;
            }
        }

        $content = file_get_contents($path);
        $regexp = '#ByteRange\[\s*(\d+) (\d+) (\d+)#'; // subexpressions are used to extract b and c

        $result = [];
        preg_match_all($regexp, $content, $result);

        // $result[2][0] and $result[3][0] are b and c
        if (isset($result[2]) && isset($result[3]) && isset($result[2][0]) && isset($result[3][0])) {
            $start = $result[2][0];
            $end = $result[3][0];
            if ($stream = fopen($path, 'rb')) {
                $signature = stream_get_contents($stream, $end - $start - 2, $start + 1); // because we need to exclude < and > from start and end
                fclose($stream);
                file_put_contents($signaturePath, hex2bin($signature));
            }
        }

        if (!file_exists($signaturePath)) {
            return false;
        }
        exec('openssl pkcs7 -in ' . $signaturePath . ' -inform DER -print_certs > ' . $signatureInfoPath . ' 2>&1', $output, $return);

        return file_get_contents($signatureInfoPath);
    }
}