Whats the different in the two?
A paludarium has a large water area in addition to a land area. People usually put small fish and aquatic plants in the water area. A vivarium is mainly land. Sometimes they will have a small water feature, but it usually isn't large enough to support fish or med.- large aquatic plants.
So people usually don't put PDF in a paludarium?
Yes, many do. Its just that you have to make sure you dont put anything in the water area that can eat your frogs(ie larger fish).