You can use the Nokia PC Suite program to export the contacts from an *.nbf file to a CSV format and then use any of the available CSV to VCF converters to get your vCard contacts file.
Convert Nokia PC Suite phone backup file to Comma Separated Value.
We found 2 software records in the database related to .nfb to .csv file format conversion.
Microsoft Windows software - convert nfb to csv on Windows
A free explorer for Nokia NBU files
Convert from nfb file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned nfb to csv. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A set of applications used to manage older Nokia mobile phones