How Can I Attach a PDF Certificate for a Membership Payment?
I don't think it's possible right now without coding.

If you are not afraid of coding, what you could do is something like :


add you membership certificate after the content of the receipt (in templates) and add an arbitrary separator between your receipt and the certificate. In my case &lt;!--break--&gt;.
use the hook_civicrm_alterMailParams with the following content (extract the part after &lt;!--break--&gt; and put it in a pdf as a attachment) :

$pos = strpos($params['html'], '&lt;!--break--&gt;');
if ($pos !== False) {
  $pdf_content = substr($params['html'], $pos + 12);
  $params['html'] = substr($params['html'], 0, $pos);

  if (empty($params['attachments'])) {
    $params['attachments'] = array();
  }
  $params['attachments'][] = CRM_Utils_Mail::appendPDF(ts('Membership certificate') . '.pdf', $pdf_content);
}



I may create a little extension for this.