There are several ways to invite a visitor.
The host in Denmark can write a letter or use a special form (a VU1, VU2 or VU3 form). If the host chooses to write a letter, the same kind of information as indicated in the form, should be provided.
You can read more about the different ways to invite a visitor on the web-site of the Danish Immigration Service
The visa applicant must submit the invitation (or the invitation ID from an on-line invitation) together with the visa application. You should not send an invitation to the Embassy.
The host should also provide applicant with a copy of the photo page of the host’s passport and a copy of the host’s Danish residence permit (if applicable).
Invitation form for visa applications (VU2):
Invitation for an application for a business visa (VU1):
Invitation for an application for a visa for cultural events, teaching sessions, courses, sport events etc.