use Barcode::DataMatrix;
use PDF::API2;
my $x = 100;
my $y = 200;
my $sz = 10;
my $mat = Barcode::DataMatrix->new()->barcode('Hello World');
my $pdf = PDF::API2->open('original.pdf');
my $page = $pdf->openpage(1);
my $content = $page->gfx();
for my $i (0 .. $#$mat) {
   for my $j (0 .. $#{$mat->[$i]}) {
      if ($mat->[$i][$j]) {
         $content->rect($x+$sz*$j, $y-$sz*$i, $sz, $sz);
      }
   }
}
$content->fill();
$pdf->saveas('modified.pdf');