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...
Do I need to register a subdomain such as blog.example.ro separately?
No, a subdomain such as blog.example.ro does not need a separate domain registration. You can configure it if you control the DNS zone for example.ro. However, adding a DNS record alone does not create a website: the hosting service must also be configured to accept that subdomain.
First, check where your DNS zone is managed and which destination the subdomain should point to. Then configure the subdomain with the service that will host its content and add the appropriate DNS record. For HTTPS access, check that the certificate also covers the subdomain.
