I can't open my decrypt Amazon Selling Partner Feed Document

I see this image when I try to read the file. Is this normal?

My code

 public function openTheFeedDocument() {

        $data = json_decode($this->getFeedDocument());

        $url = $data->payload->url;
        $iv  = base64_decode($data->payload->encryptionDetails->initializationVector);
        $key = base64_decode($data->payload->encryptionDetails->key);

        $decryptedData = openssl_decrypt(file_get_contents($url), 'AES-256-CBC', $key, OPENSSL_RAW_DATA, $iv);

        $raw_document =  mb_convert_encoding($decryptedData, 'UTF-8', 'ASCII, JIS, UTF-8, SJIS');

        echo $raw_document;
    }