Yes, you can. Adobe attaches your portfolio to their sub-domain for free. You will, however, need to purchase a custom domain. You can do it straight from your account hassle-free.
There are other alternatives that you can use as well, like GoDaddy that offers dirt-cheap domains.
Just keep in mind that the configuration process is challenging. You’ll need to edit different DNS records to make it work. In case you get stuck, Adobe’s support will be more than willing to offer help.