The only nbf to csv conversion that makes sense would be attempts to export or recover contacts from Nokia phone backups and save them to Comma Separated Value format (.csv files). This should be doable using utilities like Nokia NBU Explorer, which allow users to extract all or just some particular data from various Nokia phone backups, including .nbf files.
So it is likely that phone contacts may be exported and saved in CSV format if contacts are saved in the NBF backups.
Open NBF file Open CSV fileA free explorer for Nokia NBU files