Visa information
Please reference the below link and directly contact to the Vietnam embassy in your country.

                  http://www.projectvisa.com/visainformation/Vietnam

Invitation Letter
If you need an invitation letter for visa purposes, the organizers will be pleased to provide you with one. Delegates requiring visas should request an invitation letter from the organizers after the registration confirmation for the event. Delegates are then responsible for contacting the relevant/appropriate embassy themselves.
Required documents for the invitation letter:
Registration confirm
Passport copy