use File::Find;

my $dir = shift || '.';
find \&wanted, $dir;

sub wanted {
   next unless (-f && /\.cfm$/);
   my $newname = $File::Find::name;
   $newname =~ s/\.cfm$/.html/;
   rename $File::Find::name,$newname or die "Unable to rename $File::Find::name!";
}