use strict;
use warnings;
use Data::Dumper;

foreach my $file (glob("*.ATT")) {
    open(my $fh, '<', $file) or die "$file: $!";
    my $content = do { local $/; <$fh> };
    close($fh);

    my ( $page_id ) = $content =~ m/^page_id=(.*)/m;
    my ( $site_code ) = $content =~ m/^site_code=(.*)/m;
    my ( $subject_id ) = $content =~ m/^subject_id=(.*)/m;
    my ( $page_description ) = $content =~ m/^page_description=(.*)/m;

    next if(
        $page_id =~ m/(^\s*$|\?)/ or
        $site_code =~ m/(^\s*$|\?)/ or
        $subject_id =~ m/(^\s*$|\?)/
    );

    $page_description .= "some text - $page_id";

    $content =~ s/^page_description=.*/page_description=$page_description/m;

    print "$content";
}

##</code><code>##

OBJECT=(removed)
page_id=#### (usually 3-5 digits)
page_description=some text - #### (usually 3-5 digits)
product=(removed)
study_number=(removed)
content_provider=(removed)
site_code=###
subject_id=#########
CONTENT=test.pdf
SAVE