Viewer preferences

/*
    This file is part of the iText (R) project.
    Copyright (c) 1998-2023 Apryse Group NV
    Authors: Apryse Software.

    For more information, please contact iText Software at this address:
    sales@itextpdf.com
 */
package com.itextpdf.samples.sandbox.stamper;

import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfReader;
import com.itextpdf.kernel.pdf.PdfViewerPreferences;
import com.itextpdf.kernel.pdf.PdfWriter;

import java.io.File;

public class ChangeViewerPreference {
    public static final String DEST = "./target/sandbox/stamper/change_viewer_preference.pdf";
    public static final String SRC = "./src/main/resources/pdfs/united_states.pdf";

    public static void main(String[] args) throws Exception {
        File file = new File(DEST);
        file.getParentFile().mkdirs();

        new ChangeViewerPreference().manipulatePdf(DEST);
    }

    protected void manipulatePdf(String dest) throws Exception {
        PdfDocument pdfDoc = new PdfDocument(new PdfReader(SRC), new PdfWriter(dest));

        PdfViewerPreferences viewerPreferences = pdfDoc.getCatalog().getViewerPreferences();
        if (viewerPreferences == null) {
            viewerPreferences = new PdfViewerPreferences();
            pdfDoc.getCatalog().setViewerPreferences(viewerPreferences);
        }

        // Setting printing mode on the both sides of the pdf document (duplex mode) along with "flip on long edge" mode
        viewerPreferences.setDuplex(PdfViewerPreferences.PdfViewerPreferencesConstants.DUPLEX_FLIP_LONG_EDGE);

        pdfDoc.close();
    }
}

using System;
using System.IO;
using iText.Kernel.Pdf;

namespace iText.Samples.Sandbox.Stamper 
{
    public class ChangeViewerPreference 
    {
        public static readonly String DEST = "results/sandbox/stamper/change_viewer_preference.pdf";
        public static readonly String SRC = "../../../resources/pdfs/united_states.pdf";

        public static void Main(String[] args) 
        {
            FileInfo file = new FileInfo(DEST);
            file.Directory.Create();
            
            new ChangeViewerPreference().ManipulatePdf(DEST);
        }

        protected void ManipulatePdf(String dest) 
        {
            PdfDocument pdfDoc = new PdfDocument(new PdfReader(SRC), new PdfWriter(dest));
            
            PdfViewerPreferences viewerPreferences = pdfDoc.GetCatalog().GetViewerPreferences();
            if (viewerPreferences == null) 
            {
                viewerPreferences = new PdfViewerPreferences();
                pdfDoc.GetCatalog().SetViewerPreferences(viewerPreferences);
            }
            
            // Setting printing mode on the both sides of the pdf document (duplex mode) along with "flip on long edge" mode
            viewerPreferences.SetDuplex(PdfViewerPreferences.PdfViewerPreferencesConstants.DUPLEX_FLIP_LONG_EDGE);
            
            pdfDoc.Close();
        }
    }
}