Even the process of printing must open said file to render it for printing so unless your printer can print PDFs without use of the host PC then my answer is again no. As it stands today the file would always get opened even if we never see it happen.
Why it might have worked better in 7 has me guessing. For example the email application matters here. At the office I can right click and select print from the email app. But since I can't find what email apps were used I wonder if that's what changed.
Did you try this in Thunderbird?
I used to work on Windows 7, I use to open my email and just make a click on the attached file (PDF for example) then just a simple click on Quick Print icon and that's it, the PDF file goes directly to the printer -no need to open the file-, so NOW on Windows 8 when I make a click on the attachment and, at the time to send to the printer, the file is opened and then I need to print it from there. The thing is that I need to print several files from several email daily. What I used to take me a few minutes to do it now I take a lot of time to do finish it.