It's just a file that's been compressed with Nero. This is what is says on filext.com:
If you right click the file and select "Open with Nero BackItUp Restore", you will get a conventional "Save as..." dialog box from which you can save the file uncompressed and with its normal extension in whichever location you choose.
1. Did you backup the original files using Nero? 2. Do you have the original files somewhere? 3. If the anser to the above two questions is no then do you a) know who did back them up and b)know if they still have the original files that you gould get a copy from?