static void print_info(char const* key)
{
    char const* value = qpdf_get_info_key(qpdf, key);
    printf("Info key %s: %s\n",
	   key, (value ? value : "(null)"));
}
static void print_info(char const* key)
{
    char const* value = qpdf_get_info_key(qpdf, key);
    printf("Info key %s: %s\n",
	   key, (value ? value : "(null)"));
}