Thanks for confirming that the pdf is a binary file.

I tried with the code below (by astrobal from http://www.perlmonks.org/?node_id=1189197) but the pdf file opens with nothing:

$smtp->datasend("Content-Type: application/pdf; name=\"$attachBinaryFi
+le\"\n");
$smtp->datasend("Content-Transfer-Encoding: base64\n");
$smtp->datasend("Content-Disposition: attachment; filename=\"$attachBi
+naryFile\"\n");
$smtp->datasend("\n");
open(DAT, "$path/$attachBinaryFile") || die("Could not open binary fil
+e!");
   binmode(DAT);
   local $/=undef;
   while (read(DAT, $picture, 4096)) {
      $buf = &encode_base64( $picture );
      $smtp->datasend($buf);

   }
close(DAT);
$smtp->datasend("\n");
$smtp->datasend("--$boundary\n");
[download]

I changed "Content-Type: image/jpeg;" in his code to "Content-Type: application/pdf;".