Classic ASP: Write Binary PDF to File

The following code returns an error.  I think the problem might be related to the fact that I am trying to retrieve and write a binary PDF file.  No error is returned when I use this code to retrieve and write a text file.

<%

 url = "https://www.cl.cam.ac.uk/~mgk25/ucs/UTF-8-Plan9-paper.pdf" 
 set pdfhttp = CreateObject("MSXML2.ServerXMLHTTP") 
 pdfhttp.open "POST", url, false 
 pdfhttp.setRequestHeader "Content-Type", "application/x-www-form-urlencoded" 
 dim pdata
 pdat = "x=1&y=2&z=3" 
 pdfhttp.send pdat

 set oFs = server.createobject("Scripting.FileSystemObject")
 set oTextFile = oFs.OpenTextFile(Server.MapPath(".") & "\Test.pdf", 2, True)
 oTextFile.Write pdfhttp.responseText
 oTextFile.Close
 set oTextFile = nothing
 set oFS = nothing

 Response.Write(pdfhttp.responseText)
 Response.End

%>

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