Perkament is parchment.
In the Middle Ages, parchment was the main surface for writing. It was created from animal skin, such as sheep or calf skin. Many medieval chronicles and charters were written on parchment. Gradually, parchment was replaced by paper for most types of writing, first created from textile and later created from wood.
Charters kept being written on parchment, but were becoming less common. Nowadays, parchment and charters are rarely used, unless for ceremonial purposes.