I´ve trying to solve this problem for nearly 2 days. There are a lot of more or fewer good solutions on the net, but not a single one fits my task perfectly.
As of July 2018, there is still no answer for the OP. There is no free way to 1) silently print your pdf for a 2) closed source project.
1) You can most certainly use a process i.e. Adobe Acrobat or Foxit Reader
2) Free solutions have a GPL (GNU's General Public License). This means you must open your source code if giving the software, even for free, to anyone outside your company.
As the OP says, if you can get a PDF to Drawing.Image, you can print it with .NET methods. Sadly, software to do this also requires payment or a GPL.