use strict;
use warnings;

my $file_in = '...';
my $file_out = '...';

open(my $fh_in, '<:raw:encoding(UCS-2LE)', $file_in)
   or die("Unable to open \"$file_in\": $!\n");

open(my $fh_out, '>:raw:encoding(UCS-2LE)', $file_out)
   or die("Unable to create file \"$file_out\": $!\n");

while (<$fh_in>) {
   ...

   print $fh_out $_;
}