You cannot expect a software printer to support duplex printing.
- Duplex is a concept related to printing over real-world media, like paper.
- Digital files store a collection of pages and do not implement the concept of paper sides.
Once files are generated and you want to print them on real printer, you may then select duplex printing. You cannot order PDF or XPS file to always print in duplex, that feature is device-, driver- and OS-dependant.
A solution to your problem (debugging application) might be to install a PostScript or PCL duplex-enabled printer driver and use Print to file
feature. Once file has been generated, analyse it's content.
- PostScript is a relatively human-readable format, you should be able to find
<< /Duplex true >>
stanza or something similar (though it might depend on printer in rare cases). - PCL is a little bit more binary format, though it has a pretty readable header, you should find a string like
@PJL SET DUPLEX=ON
in the first part of the file.