#!/usr/bin/perl -w
use strict;
my $DTD_VER = "4.2"
                                                                                                                                                             
my $firstLine = <>;
                                                                                                                                                             
print $firstLine if $firstLine !~ /^\<\?xml/;
while(<>) {
        s/artlicle/book/g;
        s/DocBook XML V\d\.\d\.\d/DocBook V$DTD_VER/g;
        ...
        print $_;
}
print "</book>\n";