my %filenames = (
                 people.pdf => 'Person',
                 animal.pdf => 'animal',
                 setup.msi  => 'MSI file',
                );
...
            for (keys %filenames) {
                delete $filenames{$_} if $filename eq $_;
            }
        }
    }
    for (values %filenames) {
        print "$_ not found\n";
    }
...