Be careful about putting something down over the carpet that
will act as a "vapor barrier", i.e., something that prevents
moisture from escaping. Both roll linoleum and chair mat
plastic over a large surface area are likely to do this. If
the carpet is laid over a subfloor that emits moisture, e.g.,
concrete, and the moisture can't escape into the air, the
carpet will probably be damaged by the moisture, which you
don't want, especially if it's not your carpet.