Adobe considers this a security risk. If anyone could silently print a form without the user's knowledge then personal information could easily be stolen. You should be aware that a computer can print to any printer on a network or on the internet.
For you do this a special folder level script needs to be added to you computer and each users computer. You can then call this script from your form.
One can almost "silently" print from a document: user will only see an alert box asking him to allow or not the printing, but he will not see the Print dialog box and cannot edit any settings.
If this is what you are looking for.