In 1984, while the filming of Ghostbusters was still in progress, Dan Aykroyd and Bill Murray made a promotional film to be shown at ShoWest, a convention in Las Vegas for theater distributors. The original presentation had movie clips (without music or special effects) between the intro and outro, which have been deleted from this version. However, this article describes which clips were once there. Ray Parker Jr.'s theme song wasn't selected for the movie until after this promotion.
You can tell Aykroyd and Murray were winging it through most of the intro, but if you recall, they had years of improvisational experience together before Ghostbusters was ever a thing. No, we don't know what H.F. M. Stands for, but there are plenty of good guesses at reddit.