#!/usr/bin/perl
use strict;
use warnings;
use File::Find;
my $dir = shift;
find(\&change_ext_if_file, "$dir");

sub change_ext_if_file {
    foreach my $file ($_) {
      if (($file eq -f) && ($file =~ /.pdf$/)) {
            $file =~ s/.pdf$/.doc/;
    }
    }
    }

##</code><code>##

foreach my $file ($_) {

##</code><code>##

$file =~ s/.pdf$/.doc/;