The Nokia Backup File (.NBF format) is intended to be opened using the Nokia PC Suite app. However, the newer versions of PC Suite now use the NBU format.
Therefore, you should try using an older version of Nokia PC Suite to open the NBF file and restore the backup to your Nokia phone. You will find older versions on third party download sites.
Another alternative is to rename the .NBF file to a .ZIP file, extract the contents of the backup file using WinZip or 7Zip and manually transfer the extracted files or data from your PC to your phone.
Just change the extension from .nbf to .zip and extract using Winrar/Winzip. Here you see a list of .vcf files in the extracted folder. Connect your phone to PC using Nokia PC Suite and transfer these files to SD card or internal memory.
When I connect an external microphone to the jack, it is not working. I can see it in the "Sound" tab, but the levels is very low. I have tried with several microphones.