Hi Alison

Totara 13 and above includes evidence banks that can have have custom fields created for evidence types - One of the fields that can be created is file upload . The user or a person with evidence upload permissions can add the certificates to a user.

Another way of achieving this is to create an Open badge that can be automatically awarded and able to be displayed by the user outside of Totara detailing criteria for award in a verifiable way.

Regards