Hi @Placido11
It is not legal in any way (for good reasons) to rent an apartment in Denmark in order to use it for short term rentals. You are allowed to sublet the apartment - but only to someone that signs a normal long term (max 2 years) contract. If you live in the apartment and got your personal cpr number registered to the address you are allowed to rent it out for max 70 days (in Copenhagen).
Directly translated:
It also applies to complete subletting that the subtenant must aim to have permanent residence in the tenancy. In the case of complete subletting, you cannot therefore rent out the rental property as a holiday home via e.g. Airbnb. The conclusion is therefore, as with partial subletting, that you may not fully sublet your private rental home via Airbnb, unless it is a long-term rental agreement where the tenant registers his residence at the address.