How to recieve POST data sent using “application/octet-stream” in PHP?

Here's what I'm dealing with. One of our programs has a support form that users use to request support. What this form does is, it performs an HTTP POST request to a PHP script that's supposed to collect the info and forward it to the support e-mail address.

The POST request contains three text fields of the type Content-Type: text/plain which can be easily read in PHP using $_POST['fieldname']. Some of the content in this POST request, however, are files, of type Content-Type: application/octet-stream. Using $_POST doesn't seem to work with these files. How do I go about reading the contents of these files?

Thank you in advance.