Output a standard Base64 Encoded stream into PDF f

I am using the Royal Mail Shipping API to generate printed PDF labels, my PHP SoapClient returns a valid response shown below (only shown the initial response as the whole response is huge).

%PDF-1.7 %äãÏÒ 4 0 obj <> stream xœ endstream endobj 3 0 obj 8 endobj 9 0 obj <> stream xÚí]bì*¤Höýoübƒ¤Æ-q²É>ø%Íë‚ÔFÒ<1ÆoÌúÝú¯ý?1Æ%Èa9Ò4QÌ!}üŠ ÆãS€ZÿŸ2Mô¨H}üÃŸÇcŒ˜Z´½\¡´üý’y©1Æø$¨RÓd°úø’ÆÄŒ1Ægð´ ¨Š'ª°Z¾MCF1Æ}¥/¨{d˜ZQ•†Þ7Æ_P¢õ‘ kjŒ1.J¦ê”ÕÑŽ©,ž‹1ÆãNÿÅIü{}L%üÄcŒÑS Þª€êÁI”ÀÅÃcŒcHÚsïuP5Ð4Æ .ê2¤mbŒ1vU¼vè:ž>Æ<´¾1ÆØTŠûfÓ¢œÆcTŒ³wGF1Æ

Can anyone suggest the best method to 'convert' this Base64 encoded PDF label correctly so I can physically download this to the browser. My code below downloads the PDF file but when I attempt to open this the filesize is always 57kb and I returns the following message in Acrobat Reader

"There was an error opening this document. The file is damaged and could not be repaired."

My code is as follows:

$rm = new RoyalMailLabelRequest();
// provide shipment number, order tracking id, output format (e.g PDF/PNG)
$response = $rm->PrintLabel('TTT000358756GB', '276831601444829801', 'PDF');

header('Content-type: application/pdf');
header('Content-Disposition: attachment; filename="doc-'.$document.'.pdf"');
$data = base64_decode($response);
file_put_contents('pdf/label.pdf', $data);

UPDATE

When I try to echo the decoded response I get the following... not sure what is happening with this one.. odd.

$response = $rm->PrintLabel('TTT000358756GB', '276831601444829801', 'PDF');
$data = base64_decode($response);
echo $data;exit;

Echo'd $data response after being base64_decoded

<1uï(n?Ëzx-‡}üX¥µêÿVx7œ¡×¬¶·š›

I've also added the full base64_encode response that is returned by my code here on pastebin if it helps anyone http://pastebin.com/JEtmRURK

Sorted - been a very long day.

I didn't need to decode the response in the end so the following will work (hopefully it helps someone else doing the API integration)

function PrintLabelRequest($shipmentNumber, $transactionId)
{
   $rm = new RoyalMailLabelRequest();

   // function from library returns a response using SOAP
   $response = $rm->PrintLabel($shipmentNumber, $transactionId);

   // name the file & saved this label as a PDF in the following folder
   $filename = 'printedlabel-' . $shipmentNumber;
   file_put_contents(dirname(__FILE__) . '/labels/'. $filename .'.pdf', $response);
}