After checking the support page of Carbonite, I came to the conclusion that NTP is a file format that belongs to something else. Carbonite Backup creates its own location where it stores the files exactly as they are without assigning any file formats. Therefore, I suggest right clicking the file to see if there is mentioned the software that's needed to restore the backup. For example, in Windows, when you right click a file and go to its Properties you can see that it says (for XLS) "Microsoft Excel File". Do the same on Mac OSX, but NTP doesn't appear to be supported by Carbonite Backup.