Sending an email with pdf attachment in php - php

Question

I m new to php. I need to send the email with the pdf attachment.I m able to send an email with the attachment. But unable to open the pdf. I get the some error like this
Store information to the database(done),
Sends the staff an email with the new customer information (done), and
Send the customer a "thank you message" email with a pdf file attachment (not working).
I mean, the customer does receive an email, but when he/she opens the pdf file, I get the following error message:
"Acrobat could not oen 'file_name' because it is either not a supported file type or because the file has been damaged(for example, it was sent as an email attachment and wasn't correctly decoded)..."
If someone could help me resolve this problem, that would be great. Thanks!
Here is my code:
$to = 'form#kronova.in, ' . $Email;
$subject = 'ABC :: Admission Form Details';
$repEmail = 'form#kronova.in';
$fileName = 'ABC-Admission.pdf';
$fileatt = $pdf->Output($fileName, 'E');
$attachment = chunk_split($fileatt);
$eol = PHP_EOL;
$separator = md5(time());
$headers = 'From: Principal abc <'.$repEmail.'>'.$eol;
$headers .= 'MIME-Version: 1.0' .$eol;
$headers .= "Content-Type: multipart/mixed; boundary=\"".$separator."\"";
$message = "--".$separator.$eol;
$message .= "Content-Transfer-Encoding: 7bit".$eol.$eol;
$message .= "Thanks for filling online application form. Your online admission registration number is E0000". mysql_insert_id() . "." .$eol;
$message .= "--".$separator.$eol;
$message .= "Content-Type: text/html; charset=\"iso-8859-1\"".$eol;
$message .= "Content-Transfer-Encoding: 8bit".$eol.$eol;
$message .= "--".$separator.$eol;
$message .= "Content-Type: application/pdf; name=\"".$fileName."\"".$eol;
$message .= "Content-Transfer-Encoding: base64".$eol;
$message .= "Content-Disposition: attachment".$eol.$eol;
$message .= $attachment.$eol;
$message .= "--".$separator."--";
if (mail($to, $subject, $message, $headers)){
echo "Email sent";
}
else {
echo "Email failed";
}