I don't use this software but a bit of web-searching suggests that NTI make two separate pieces of software. One is CD&DVD Maker, the other is BackUpNow! Although they are separate, they may appear together, as part of a 'suite' of software.
NBF files appear to be compressed back-up files, produced by BackUpNow!, rather than by CD&DVD Maker. This suggests that, somewhere in the burning process, you've clicked a 'back-up' button, rather than a 'copy' one.
I'm sorry that's a bit vague but I suggest burning again but double-checking the options that you're selecting as you do so.
Chris