Thank you thanos1983.

This is what I have tried:

use strict;
use Net::SMTP;
use MIME::Base64;
 
my $smtphost = 'some_smtp_host';
my $username = 'some_username';
my $password = 'some_password';
my $emailto = 'to@hello.com';
my $emailfrom = 'from@hello.com';
my $subject = 'Hello world';
my $message = 'Test message';

sub date_r {
    my ($monthday, $mon, $yr, $ time, $hour, $str);
    my (@lt) = ();

    @lt = localtime();
    $monthday = $lt[3];
    $mon = $lt[4]+1;
    $yr = $lt[5] + 1900;
    $hour = $lt[2];
    $time = sprintf("%02d:%02d:%02d", $hour, $lt[1], $lt[0]);
    $str = $mon . '/' .$monthday . '/' . $yr . ' ' . $time;
    return $str;
}

my $smtp = Net::SMTP->new($smtphost, Debug => 1, Timeout => 5);

$smtp->datasend("AUTH LOGIN\n");
$smtp->datasend(encode_base64($username));
$smtp->datasend(encode_base64($password));

$smtp->mail($emailfrom);
$smtp->to($emailto);

$smtp->data();

my $boundary = 'frontier';
my $attachBinaryFile = 'helloworld.pdf';
$smtp->datasend("MIME-Version: 1.0\n");
$smtp->datasend("Content-type: multipart/mixed;\n\tboundary=\"$boundar
+y\"\n");
$smtp->datasend("--$boundary\n");
$smtp->datasend("Content-type: text/plain;\n");
$smtp->datasend("\nSome plain text here in the body of the email\n");
$smtp->datasend("\n");
$smtp->datasend("--$boundary\n");
$smtp->datasend("Content-Type: application/pdf; charset=utf-8; name=\"
+$attachBinaryFile\"\n");
$smtp->datasend("Content-Disposition: attachment; filename=\"$attachBi
+naryFile\"\n");
$smtp->datasend("Content-Transfer-Encoding: 8bit\n");
my $pdfbody = do {
    local $/;
    open my $fh ,'<', "/path/helloworld.pdf" or die "pdfread: $!";
    <>;
}; 
$smtp->datasend("\n");
$smtp->datasend("$pdfbody\n");
$smtp->datasend("--$boundary\n");
$smtp->dataend();
$smtp->quit;
[download]

I do get the email message and the pdf attachment in the email. But I am not able to open the pdf attachment - some sort of data corruption.

Please help.