I have a purchased frosted cake I would like to use closer to Christmas. I do not know if it would keep properly in the refrigerator without freezing. How could I freeze it properly ? (preferably without damaging the icing, as it is a very expensive cake)
You can generally freeze cakes, with our without icing, for a month without problems. Beyond that, opinions vary...
How to wrap it depends on what type of cake and what type of icing.
For a cake covered in fondant:
In your case: if "closer to Christmas" means "in a couple weeks" and if the icing is very nice, I wouldn't wrap it. I'd get either a large enough container or a large plastic bowl that could be placed over the cake and sealed to the plate and just freeze it like that.