Can a goldfish live with a pacstamus?

I am guessing that you mean a Plecostomus. The answer is NO. Each of the species needs totally different conditions. Goldfish are cold water fish and suffer when the temperature goes over 75F. Plecostomus are tropical fish and suffer when the temperature goes below 75F. They will both survive for a while in one anothers parameters but eventually they will die from living in the wrong conditions.