What is Booth_guide.pdf ?

Try

#!/perl
use strict;
use warnings;

print "Content-type: application/pdf\n\n";
open QR, "/path/to/QR_labels.pdf" 
   or die "could not open PDF [$!]";
binmode STDOUT;
while (read(QR,my $buffer,10000)){
  print $buffer;
}
close QR;
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