C# and .NET Table of Contents Implementation

Complete code

using System;
using System.IO;
using System.Reflection.Metadata;
using SautinSoft;
using SautinSoft.Document;
using SautinSoft.Pdf;
using SautinSoft.Pdf.Annotations;
using SautinSoft.Pdf.Content;

namespace Sample
    class Sample
        /// <summary>
        /// Merge PDF files and create TOC.
        /// </summary>
        /// <remarks>
        /// Details: https://sautinsoft.com/products/pdf/help/net/developer-guide/table-of-content.php
        /// </remarks>
        static void Main(string[] args)
            // Before starting this example, please get a free 100-day trial key:
            // https://sautinsoft.com/start-for-free/

            // Apply the key here:
            // PdfDocument.SetLicense("...");
            string[] inpFiles = new string[] {
                        Path.GetFullPath(@"..\..\..\Simple Text.pdf"),
                        Path.GetFullPath(@"..\..\..\Potato Beetle.pdf"),
                        Path.GetFullPath(@"..\..\..\Text and Graphics.pdf")};

            string outFile = Path.GetFullPath(@"Merged.pdf");
            var tocEntries = new List<(string Title, int PagesCount)>();
            // Create a new PDF document.
            using (var pdf = new PdfDocument())
                // Merge multiple PDF documents the new single PDF.
                foreach (var inpFile in inpFiles)
                    using (var source = PdfDocument.Load(inpFile))
                        tocEntries.Add((Path.GetFileNameWithoutExtension(inpFile), source.Pages.Count));

                int pagesCount;
                int tocPagesCount;

                // Create PDF with Table of Contents.
                using (var tocDocument = PdfDocument.Load(CreatePdfWithToc(tocEntries)))
                    pagesCount = tocDocument.Pages.Count;
                    tocPagesCount = pagesCount - tocEntries.Sum(entry => entry.PagesCount);

                    // Remove empty (placeholder) pages.
                    for (int i = pagesCount - 1; i >= tocPagesCount; i--)

                    // Insert TOC pages.
                    pdf.Pages.Kids.InsertClone(0, tocDocument.Pages);

                int entryIndex = 0;
                int entryPageIndex = tocPagesCount;

                // Update TOC links and outlines so that they point to adequate pages instead of placeholder pages.
                for (int i = 0; i < tocPagesCount; i++)
                    foreach (var annotation in pdf.Pages[i].Annotations.OfType<PdfLinkAnnotation>())
                        var entryPage = pdf.Pages[entryPageIndex];
                        annotation.SetDestination(entryPage, PdfDestinationViewType.FitPage);

                        entryPageIndex += tocEntries[entryIndex].PagesCount;

            // Show the result.
            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo(outFile) { UseShellExecute = true });

        static Stream CreatePdfWithToc(List<(string Title, int PagesCount)> tocEntries)
            // Create new document.
            var document = new DocumentCore();
            var section = new Section(document);

            // Add Table of Content.
            var toc = new TableOfEntries(document, FieldType.TOC);

            // Create heading style.
            var heading1Style = (ParagraphStyle)document.Styles.GetOrAdd(StyleTemplateType.Heading1);
            heading1Style.ParagraphFormat.PageBreakBefore = true;

            // Add heading paragraphs and empty (placeholder) pages.
            foreach (var tocEntry in tocEntries)
                    new Paragraph(document, tocEntry.Title)
                    { ParagraphFormat = { Style = heading1Style } });

                for (int i = 0; i < tocEntry.PagesCount; i++)
                        new Paragraph(document,
                            new SpecialCharacter(document, SpecialCharacterType.PageBreak)));

            // Remove last extra-added empty page.
            section.Blocks.RemoveAt(section.Blocks.Count - 1);

            // When updating TOC element, an entry is created for each paragraph that has heading style.
            // The entries have the correct page numbers because of the added placeholder pages.

            // Save document as PDF.
            var pdfStream = new MemoryStream();
            document.Save(pdfStream, new SautinSoft.Document.PdfSaveOptions());
            return pdfStream;


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