A free example of an invitation letter shows how a formal invitation should be laid out properly. A good example letter includes all of the information that should be included, along with a customizable format.
Invitation letters should include the company letterhead, date, and a short direct introduction. The benefits of accepting the invitation should be explained in the beginning of the letter. A description of the company and what the company does should follow. Further detail are added after the company description. A sincere closing with a thank you, and how to contact the company for further details finishes the letter.