You can register .ro domains and every Romanian extension (.com.ro, .info.ro, .org.ro, .store.ro and more), plus international ones such as .com, .net, .org, .e...
Usually, you do not add it to your domain's regular DNS zone. A PTR record provides a reverse lookup, mapping an IP address to a hostname. It is managed by the provider that controls the IP address, or by an administrator responsible for a delegated reverse DNS zone.
If you manage a mail server, check with your server or IP address provider about configuring reverse DNS. The hostname specified in the PTR record should itself have an A or AAAA record pointing back to that IP address. A correctly configured PTR record can matter during checks by receiving mail servers, but it does not guarantee inbox delivery.