All souls are immortal. But, while karmas* are still attached to the souls, the souls occupy into various types of bodies, like the humans, the animals, the birds, the plants, etc. The body and the soul are different things. When all the attached karmas are destroyed the soul is liberated from the body permanently and reaches to the top of universe, called Siddh Shila and stays there forever. These souls then are called Siddhas. That is the state of being our Immortal soul from the bondage of the body.