When I was in Copenhagen last year, I couldn't find any normal restaurants that would take my US Mastercard. They all wanted ones with a chip in it, which mine did not have.

I'd hope that they have some ATMs that would take your card, but I didn't try. My hotel did accept a normal MC.

The airport exchange is a horrid rip off. I changed $100 US, and the place had a tiny text on their display about a transaction fee. So a big sign with a "No Commission", and then the transaction fee. I think it ended up costing me 10% or so total over normal interchange fees. I would have paid 2% if I had found an ATM instead. I was pretty tired, or otherwise I would have refused the transaction.