How about just testing the pdf as a standalone file too?

open(FF, ">","/tmp/holamundo.pdf");
print FF $pdf->Finish();
close(FF);
[download]

and view that pdf view a viewer, or drag and dropping into your browser?

I created a small testcase (using miniserver.pl), and your pdf is displayed inline in the browser, with barcode and all, no problems. (at first I thought you needed extra mime encoding). It maybe the browser?

print $client "HTTP/1.0 200 OK", Socket::CRLF;
print $client "Content-type: application/pdf", Socket::CRLF; #view pdf
+ inline
#print $client "Content-type: application/x-unknown", Socket::CRLF; # 
+force a save popup
print $client Socket::CRLF;
my $SLURP  = `$localfile`;
print $client $SLURP;
[download]