Accepting a full PDF via submitForm with PHP

I've got a button that has this code:

var myDoc = event.target;
myDoc.submitForm({
cURL: "http://myserver/submitpdf.php#PDF",
cSubmitAs: "PDF",
cPermID: myDoc.docID[0],
cInstID: myDoc.docID[1],
cUsageRights: submitFormUsageRights.RMA
});

and this PHP written on the server (this script writes to a simple text log what it's getting and when whenever a request is made to submitpdf.php):

<?php

foreach($_REQUEST as $k => $v) {
$postarray .= $k . "=" . $v . "&";
}
foreach($_FILES as $h => $z) {
$postarray .= $h . "=" . $z . "&";
}

$data = "time: " . date("d/m/y : H:i:s", time()) . " | PostedVariables=" . $postarray . "\n";
$file = "log.txt";
if (!$file_handle = fopen($file,"a")) { echo "Cannot open file"; }
if (!fwrite($file_handle, $data)) { echo "Cannot write to file"; }
fclose($file_handle);

?>

When I run it cSubmitAs FDF - I see in the log a POSTed variable called topmostSubform=Array& which represents the data. So, it works.

However, when I submit as PDF I don't get anything in GET, POST or FILES. I'm quite perplexed. Any ideas?

Thanks in advance for your help.

Jason