use Archive::Zip qw(:ERROR_CODES :CONSTANTS);

my $zip = Archive::Zip->new();
	
$fileToAdd = '12345678.pdf';

# ...etc...
# ...etc...
# ...etc...

$fileWithPath = "$viewBillPath\\$fileToAdd";

$zip->addFile($fileWithPath) or die "couldnt add $viewBillPath\\$fileToAdd\n";