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

foreach my $file (glob("*.ATT")) {
    open(my $fh, '<', $file) or die "$file: $!";
    my %params = map {
        chomp($_);
        my ($key, $value) = split(/=/, $_);
        $value="" unless(defined($value));
        ($key, $value) 
    } <$fh>;
    close($fh);
    next if(
        $params{'page_id'} =~ m/(^\s*$|\?)/ or
        $params{'site_code'} =~ m/(^\s*$|\?)/ or
        $params{'subject_id'} =~ m/(^\s*$|\?)/
    );

    $params{'page_description'} .= "some text - $params{'page_id'}";
    print Dumper(\%params);
}

##</code><code>##

$VAR1 = {
          'content_provider' => '(removed)',
          'page_id' => '#### (usually 3-5 digits)',
          'OBJECT' => '(removed)',
          'SAVE' => '',
          'study_number' => '(removed)',
          'CONTENT' => 'test.pdf',
          'page_description' => 'some text - #### (usually 3-5 digits)',
          'subject_id' => '#########',
          'site_code' => '###',
          'product' => '(removed)'
        };