NIV
Every day he walked back and forth near the courtyard of the harem to find
out how Esther was and what was happening to her.
NIVUK
Every day he walked to and fro near the courtyard of the harem to find out
how Esther was and what was happening to her.
https://www.biblegateway.com/verse/en/Esther%202%3A11
It doesn’t really mean anything different. The archaic fro occurs only in
that phrase. It used to be by far the most common way to say that, but no
longer is: see this Google N-gram:
https://english.stackexchange.com/questions/119500/whats-the-difference-between-to-and-fro-and-back-and-forth