In olden days, office workers made carbon copies and photocopies
of documents, and these copies had to be manually filed in file
cabinets. In Word, the "print to file" option prints a paper
copy that automatically files itself in the proper place in the
file cabinet, thereby saving office workers many hours of tedious
labor and increasing office productivity.
It produces a file (with the extension ".prn") that contains
all of the commands that Word would have sent to the printer
in binary format. The use is ancient and reaches back to the
days of MSDOS