62mm,100mm
         ---------------------
        |                     |
        |   This is your      |
        |                     |
        |   textblock         |
        |                     |
        |   foo bar baz       |
        |                     |
        |   end.              |
        |                     |
 0,$ypos|.....................|
        |                     |
        |                     |
        |                     |
        |                     |
         ---------------------
      0,0

##</code><code>##

...
my ($endw, $ypos) = $tb->apply;

$page->mediabox(0, $ypos,  62/mm, 100/mm);    # <---

$pdf->save;
$pdf->end;