Capture response stream and output to file - asp.net

Question

We are using an online pdf encoding service where we send them the raw html and they return the pdf document. We want to take the WebResponse and immediately download it as a file to their desktop. This seems so straightforward and yet I can't seem to capture the stream correctly for download. I've tried many different approaches but I always end up with a 0 byte file for download. This is my latest incarnation which has gotten overly complicated but it still doesn't work.
Dim request = DirectCast(HttpWebRequest.Create(Url), HttpWebRequest)
request.Method = "POST"
request.ContentType = "application/x-www-form-urlencoded"
request.ContentLength = byteArray.Length
Using dataStream = request.GetRequestStream()
dataStream.Write(byteArray, 0, byteArray.Length)
End Using
Try
Dim response As WebResponse = request.GetResponse
Dim bytes As Byte()
Using st As Stream = response.GetResponseStream
Dim ByteList As New ArrayList
Dim reader As New BinaryReader(st)
Dim length As Integer
While (InlineAssignHelper(bytes, reader.ReadBytes(1024))).Length > 0
ByteList.Add(bytes)
length += bytes.Length
bytes = New Byte(length - 1) {}
Dim position As Integer = 0
For Each b As Byte() In ByteList
Array.Copy(b, 0, bytes, position, b.Length)
position += b.Length
Next
End While
End Using
HttpContext.Current.Response.Clear()
HttpContext.Current.Response.AddHeader("Content-Type", "application/pdf")
HttpContext.Current.Response.AddHeader("Content-Disposition", String.Format("{0}; filename=Report Detail.pdf; size={1}", "attachment", bytes.Length.ToString()))
HttpContext.Current.Response.BinaryWrite(bytes)
HttpContext.Current.Response.Flush()
HttpContext.Current.Response.Close()
HttpContext.Current.Response.End()
Private Shared Function InlineAssignHelper(Of T)(ByRef target As T, ByVal value As T) As T
target = value
Return value
End Function