Adventures in hatmaking: Edwardian hat, part 2, Buckram question

I have never worked with buckram before and now I am faced with this, probably ridiculusly easy, question; "How do I flatten it?". The buckram I bought was send to me by mail, in order to fit in an envelope it has been folded... Before I can work with it, it needs to be flat! And I have really no clue at all whether or not I can iron it. I feel really silly...

So fellow costume - and hatmakers help me out! How can I flatten buckram.