Represents the "Duplex" entry of the viewer preferences dictionary object.

It is an optional entry defined as part of the PDF 1.7 specification.

It contains a string representing a PDF name object.

This item may take one of the following valid values:.

• Simplex
• DuplexFlipShortEdge
• DuplexFlipLongEdge

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 150, page 364.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 8.1, page 28.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 147, page 437.

Advises the printer driver on duplex printing. Simplex prints one side per sheet; DuplexFlipShortEdge and DuplexFlipLongEdge request two-sided printing with the sheet flipped along the short or long edge respectively.