You might want to look at these two third-party examples (I have not tried them) : these show how to use Microsoft Powershell (actually it's just using Adobe Acrobat as a program) and Java to print a PDF to the default printer; in theory you could wrap up these in a PRPC Activity* - assuming it would be acceptable to issue the print job from the back-end not the the user's desktop ?
If you are running PRPC in Linux environment; you might want to use some the 'pdf2dsc' commandline (to convert PDF to PostScript, which you should then be able to print. (again: I have not tried this).
It sounds like you are working with PDFBytes rather than PDFFiles here: so you would need to write these bytes to a temporary file (probably) before using any of these approaches.
* I'm also not entirely sure of the best way of 'wrapping' up a Powershell call from Java: but you could perhaps create a Powershell script to 'poll' for a file on-disk (created by a PRPC Activity File Connector maybe).
We have tried below code and seems to be working in eclipse. When we tried importing JAR(java-rt-jar-stubs-1.5.0.jar) containing javax.print.* and java.awt.print.*, we are getting UNKNOWN archive type error. Except this we are good with code.