How to get data sent using WebClient.UploadData

I am trying to load some data from an ActiveX control into a webpage. The best way to do this is in a byte array via WebClient.UploadData.

I'm having trouble finding how I can get my data into pageload ... There are many examples of how to send data, but I haven't found one yet that shows how to get data to a web server ...

Can anyone point me in the right direction?