Hi,
You can not format the post data directly. You can only use file PostDataItem. The code will be something like this:
Code: C#
request.PostData.Add(new PostDataItem(full_path_of_the_file));
This will create a new PostDataItem with its Type property set to "File". The reason is the actual formatting/posting is done asynchronously by the browser engine. So you can only provide the file name.
Thanks!