carbon paper 
noun [mass noun]
Thin paper coated with carbon or another pigmented substance, used for making a second impression of a document as it is being written or typed.Documents are copied with carbon paper and then held together by straight pins; staplers are largely unknown....
- If possible, that information should also be transferred to the assigned allocation by using pressure sensitive paper or carbon paper inside the envelope.
- He grumpily announced that he wasn't going to argue with me (which was nice) and let me write down my chosen price and credit card number on his carbon paper and moved on.