As @LuisScott said, you don't need DocuSign API to do this. You would be better suited using DocuSign Connect. Much easier, you do not need to get code approval from DocuSign either.
DocuSign API is for modifying how DocuSign displays or modifies documents. In other words, pre-processing the envelope.
DocuSign Connect is for post-processing the envelope - which is what you want to do by your own account.
I had a similar question not too long ago that was answered here:
DocuSign Custom Connect - How to make a listener in php example?
Sample listener code:
https://github.com/docusign/docusign-soap-sdk/blob/master/PHP/Connect/index.php
My sample code to pull out form data:
// Figure out the URL of this server
// NOTE: DocuSign only pushes status to HTTPS!
$postBackPath = empty($_SERVER['HTTPS']) ? 'http://' : 'https://';
$postBackPath .= ($_SERVER['SERVER_NAME'] . ':' . $_SERVER['SERVER_PORT'] . $_SERVER['REQUEST_URI'] );
$postedXml = @file_get_contents('php://input');
if(!empty($postedXml)) {
// see if this is a post to this page if it is then we have to save it.
$xml = simplexml_load_string($postedXml);
$post = $xml;
print 'Got Envelope ID: ' . $xml->EnvelopeStatus->EnvelopeID . '<br />';
}
foreach($post->EnvelopeStatus->RecipientStatuses->RecipientStatus->FormData->xfdf->fields->children() as $element) {
foreach($element->attributes() as $a) {
$fieldArray[(string)$a] = (string)$element->value;
}
}
From there, you can do whatever you want with the data.
However, you do have to play around with some settings in DocuSign to get this to work. In particular, in the settings menu there is a DocuSign connect menu, where you can specify where your listener script is, what information you want passed (field data in your case), and when do you want data sent to the script (when envelope is completed).
Also, you have to have DocuSign Connect enabled for your account. If you have API access, you will have access to it as well but sometimes they need to turn it on for you.