Convert NBU to NBF

Software utilities such as Nokia NbuExplorer allow users to work both with the NBU and NBF files. Unfortunately it doesn't seem to be possible to convert between each another. You can however just recover whatever you need from the backup, like contacts and use it in your new phone. But a successful direct nbu to nbf conversion is unlikely.

Simply put, it is impossible to convert NBU to NBF directly.
Thus, there is no so-called nbu to nbf converter or a free online .nbu to .nbf converter to be found.