Attending Catholic mass after many years away

Say there's a once-Catholic adult who is considering attending a Catholic mass. This person was baptized Catholic as a baby, and received first communion when a child. This person did not go through the confirmation process, as their family has moved away from the church by that time. If this person plans to attend a Catholic mass, would they be expected to/would it be appropriate to receive communion? Would they need to do anything before just showing up? This person might rejoin the Catholic faith but wishes to attend a mass at Christmas. After so many years away (30?) this person would like to see what a mass is like, once again.