User281315223 posted
Generally this is something that is out of the control of a web application, so it may / may not be possible.
Usually, it is up to the user to indicate that the contents should be printed in duplex (if the printer itself supports that). However, you may be able to explicitly create a PrintDocument and set the CanDuplex property to true to handle the printing as
mentioned in this related MSDN article and this related discussion:
YourPrintingDocumentObject.PrinterSettings.CanDuplex = true;
