Those strange demons are always carrying about secret information around with them. Occasionally some of this information turns out to be very important and in some way related to hell. Most of the time though, the only thing the folder contains is a few shopping lists and maybe a magazine or two.
The 'N' bit of its title is thought to stand for 'No longer applicable' and the '666' is thought to refer to Satan's battalion of idiotic unusable minions. This folder is therefore proof of the failure of the devil's advocate to do anything properly evil.