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.
The most flexible, easiest and best performing method I could find was using GhostScript. It can print to windows printers directly by printer name.
"C:\Program Files\gs\gs9.07\bin\gswin64c.exe" -dPrinted -dBATCH -dNOPAUSE -sDEVICE=mswinpr2 -dNoCancel -sOutputFile="%printer%printer name" "pdfdocument.pdf"
Add these switches to shrink the document to an A4 page.
-sPAPERSIZE=a4 -dPDFFitPage