Set a ViewerPreferences dictionary entry in an output PDF file.
void xpdfSpliceSetViewerPreferenceName(XpdfSpliceOutputHandle out, const char *key, const char *val)
This function sets a ViewerPreferences dictionary entry (with a name-type value) in an output PDF file. The entry specified by key is set to val.

The PDF specification lists the available viewer preferences. This function only handles preferences whose values are name objects.

XpdfSpliceOutputHandle out; out = xpdfSpliceOpenOutput("c:/test/output.pdf"); xpdfSpliceSetViewerPreferenceName(out, "Duplex", "DuplexFlipLongEdge"); ...