In Denmark you can choose to become registrered as a company at any time. But if you turnover is above 50.000 Danish kroners, then you by law have to become registered. If your turnover is less than 50.000 Danish kroners, you dont have to register, but you can chose to do it if you wish.
In praxis what you do is to fill out the ”momsregistrerings blanketten”. Fill out the blanks, and send it in to your local tax office. You can find adresses at skat.dk.
About two weeks later you will recieve you Vat number (SE/CVR#), and you will be ready to do business in Denmark.
Remember that you have to report how much vat (moms) you have turned over, every quarter. By the 1st of July in the following year, you have to send in your tax papers (udvidede selvangivelse), and inform the tax office of your revenue or losses.
To learn more about starting a business in denmark you can call Skat at 72221818.