@Jaime Núñez Thank you for asking.
There must be a reason you would like to make a subdomain a managed domain. Microsoft makes this possible. So Yes!
However, the managed domain prerequisite should be met on the selected system. So far you can find An Azure Active Directory Domain Services managed domain enabled and configured in your Azure AD tenant. Then, you're good to go.
In addition, try to understand the administrative tasks that you can do and those you can not do on managed domain.
You can read more about Azure: Active Directory Domain Services (Managed Domain) and how to create managed VM
Hope this is helpful!
Success.