Yes - the PDF is already generated!
OK - your suggestion helped - I had lots of redundant things there - but I think the actual problem was the PDF. When I used a locally created base64 PDF things worked…
So for others who need to do this…
<cfhttp url="#theURL#" charset="utf-8" method="post" getasbinary="auto" result="myFile" > <cfhpptparam>s etc dataArray = deserializeJSON(myFile.filecontent); decode = binaryDecode(dataArray.response, "base64"); header name="Content-disposition" value="inline" ; content variable = decode type="application/pdf";