This observation was helpful. It helped me understand what might be happening. It's pretty tough to troubleshoot when one has no clear understanding of the problem. I had noticed that it lacked the PDF header that I was expecting, but it was your observation that helped me understand why. Thank you. As it turns out, this problem had nothing to do with the download's initiation, only with its quality during the transfer. For the full solution of what I found to work, and not work, see my own answer (to be posted shortly).