No, sites hosted on wp.com cannot add such adverts.
You need to have both your own domain and your own (paid for by you) web host. You can use wp.ORG software for free but you pay for both name and hosting.
Right now you have a domain mapping upgrade which changes only your url (changes only the name). With domain mapping, your site / blog is still hosted for free on wordpress.com. Your use of the wp.com as a host for free means that you must abide by the same terms of service as if you had not purchased a domain name.