One of the Primex offices is situated on the ground floor of Imperial Hotel. You can see where the currency exchange office is here. In no case, exchange money in hotels. All the hotels make money on currency exchange transactions, therefore, they will definitely offer you bad rates. For example, in the city you will be given 7.5 DKK per euro, whereas the hotel will give you only 6 DKK. Thus, you can lose 150 DKK per 100 euros, which is 20 euros.
In Denmark you will have to face the fact that despite being a member of the EU since 1979, it still has its local currency, Danish crown, not euro. This is related to two 2 factors: according to the constitution of 1953, only the royal house is entitled to print the Danish money. Therefore, transiting to euro they would have to change the constitution. The second factor is the fact that the Danes convincingly voted against the introduction of euro as the main currency at the referendum in 2000. Therefore, it can be easily proclaimed that the Danish people prefer their own currency, Danish crowns, but euros are accepted in most places. If you do not want to worry about this topic – where the exchange rate is better, whether to change or not to change – there is an alternative: paying by your credit card, though it also has its specifics.
I would even say that that payment by credit cards is accepted everywhere, but not all the credit cards are accepted. Owing to some reasons, foreign credit cards are not welcomed by many stores. I suppose that it is related to the bank charges, which the outlet has to pay in case of purchase payment by credit cards and thus many of them just do not want to deal with that. So I would advise to get some cash. In some places payment by credit cards is permitted provided a purchase of over 100 DKK, which is gain related to the bank charges.
By the way, the tips are normally included into the bill and they should not be left. If you leave the tips, it means you are not local, since the Danes hardly ever do it. It is thought that the Danish people earn enough, since they have some of the highest salaries in Northern Europe.
Enjoy your time in Copenhagen!