PM> Install-Package Spire.PDF

using Spire.Pdf;
using Spire.Pdf.Actions;
using Spire.Pdf.Interactive.Annotations;
using Spire.Pdf.Destinations;
using Spire.Pdf.Graphics;
using System;
using System.Drawing;

namespace TableOfContents
{
    internal class Program
    {
        static void Main(string[] args)
        {
            //Initialize an instance of the PdfDocument class
            PdfDocument doc = new PdfDocument();
            //Load a PDF document
            doc.LoadFromFile("Sample.PDF");

            //Get the page count of the document
            int pageCount = doc.Pages.Count;

            //Insert a new page into the pdf document as the first page
            PdfPageBase tocPage = doc.Pages.Insert(0);

            //Draw TOC title on the new page
            string title = "Table of Contents";
            PdfTrueTypeFont titleFont = new PdfTrueTypeFont(new Font("Arial", 20, FontStyle.Bold));
            PdfStringFormat centerAlignment = new PdfStringFormat(PdfTextAlignment.Center, PdfVerticalAlignment.Middle);
            PointF location = new PointF(tocPage.Canvas.ClientSize.Width / 2, titleFont.MeasureString(title).Height + 10);
            tocPage.Canvas.DrawString(title, titleFont, PdfBrushes.CornflowerBlue, location, centerAlignment);

            //Draw TOC content on the new page
            PdfTrueTypeFont titlesFont = new PdfTrueTypeFont(new Font("Arial", 14));
            String[] titles = new String[pageCount];
            for (int i = 0; i < titles.Length; i++)
            {
                titles[i] = string.Format("This is page {0}", i + 1);
            }
            float y = titleFont.MeasureString(title).Height + 10;
            float x = 0;

            //Draw page numbers of the target pages on the new page
            for (int i = 1; i <= pageCount; i++)
            {
                string text = titles[i - 1];
                SizeF titleSize = titlesFont.MeasureString(text);

                PdfPageBase navigatedPage = doc.Pages[i];

                string pageNumText = (i + 1).ToString();
                SizeF pageNumTextSize = titlesFont.MeasureString(pageNumText);
                tocPage.Canvas.DrawString(text, titlesFont, PdfBrushes.CadetBlue, 0, y);
                float dotLocation = titleSize.Width + 2 + x;
                float pageNumlocation = tocPage.Canvas.ClientSize.Width - pageNumTextSize.Width;
                for (float j = dotLocation; j < pageNumlocation; j++)
                {
                    if (dotLocation >= pageNumlocation)
                    {
                        break;
                    }
                    tocPage.Canvas.DrawString(".", titlesFont, PdfBrushes.Gray, dotLocation, y);
                    dotLocation += 3;
                }
                tocPage.Canvas.DrawString(pageNumText, titlesFont, PdfBrushes.CadetBlue, pageNumlocation, y);

                //Add actions that will take you to the target pages when clicked on to the new page
                location = new PointF(0, y);
                RectangleF titleBounds = new RectangleF(location, new SizeF(tocPage.Canvas.ClientSize.Width, titleSize.Height));
                PdfXYZExplicitDestination Dest = new PdfXYZExplicitDestination(navigatedPage, -doc.PageSettings.Margins.Top, -doc.PageSettings.Margins.Left);
                PdfLinkAnnotation action = new PdfLinkAnnotation(tocPage, titleBounds, new PdfGoToAction(Dest));
                action.Border.Width = 0;
                PdfAnnotationCollection.Create(tocPage).Add(action);
                y += titleSize.Height + 10;
            }

            //Save the result pdf document
            doc.SaveToFile("AddTableOfContents.pdf");
            doc.Close();
        }
    }
}

Imports Spire.Pdf
Imports Spire.Pdf.Actions
Imports Spire.Pdf.Interactive.Annotations
Imports Spire.Pdf.Destinations
Imports Spire.Pdf.Graphics
Imports System.Drawing

Namespace TableOfContents
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Initialize an instance of the PdfDocument class
            Dim doc As PdfDocument = New PdfDocument()
            'Load a PDF document
            doc.LoadFromFile("Sample.PDF")

            'Get the page count of the document
            Dim pageCount As Integer = doc.Pages.Count

            'Insert a new page into the pdf document as the first page
            Dim tocPage As PdfPageBase = doc.Pages.Insert(0)

            'Draw TOC title on the new page
            Dim title = "Table of Contents"
            Dim titleFont As PdfTrueTypeFont = New PdfTrueTypeFont(New Font("Arial", 20, FontStyle.Bold))
            Dim centerAlignment As PdfStringFormat = New PdfStringFormat(PdfTextAlignment.Center, PdfVerticalAlignment.Middle)
            Dim location As PointF = New PointF(tocPage.Canvas.ClientSize.Width / 2, titleFont.MeasureString(title).Height + 10)
            tocPage.Canvas.DrawString(title, titleFont, PdfBrushes.CornflowerBlue, location, centerAlignment)

            'Draw TOC content on the new page
            Dim titlesFont As PdfTrueTypeFont = New PdfTrueTypeFont(New Font("Arial", 14))
            Dim titles = New String(pageCount - 1) {}
            For i = 0 To titles.Length - 1
                titles(i) = String.Format("This is page {0}", i + 1)
            Next
            Dim y As Single = titleFont.MeasureString(title).Height + 10
            Dim x As Single = 0

            'Draw page numbers of the target pages on the new page
            For i = 1 To pageCount
                Dim text = titles(i - 1)
                Dim titleSize As SizeF = titlesFont.MeasureString(text)

                Dim navigatedPage As PdfPageBase = doc.Pages(i)

                Dim pageNumText As String = (i + 1).ToString()
                Dim pageNumTextSize As SizeF = titlesFont.MeasureString(pageNumText)
                tocPage.Canvas.DrawString(text, titlesFont, PdfBrushes.CadetBlue, 0, y)
                Dim dotLocation = titleSize.Width + 2 + x
                Dim pageNumlocation As Single = tocPage.Canvas.ClientSize.Width - pageNumTextSize.Width
                For j = dotLocation To pageNumlocation - 1
                    If dotLocation >= pageNumlocation Then
                        Exit For
                    End If
                    tocPage.Canvas.DrawString(".", titlesFont, PdfBrushes.Gray, dotLocation, y)
                    dotLocation += 3
                Next
                tocPage.Canvas.DrawString(pageNumText, titlesFont, PdfBrushes.CadetBlue, pageNumlocation, y)

                'Add actions that will take you to the target pages when clicked on to the new page
                location = New PointF(0, y)
                Dim titleBounds As RectangleF = New RectangleF(location, New SizeF(tocPage.Canvas.ClientSize.Width, titleSize.Height))
                Dim Dest As PdfXYZExplicitDestination = New PdfXYZExplicitDestination(navigatedPage, -doc.PageSettings.Margins.Top, -doc.PageSettings.Margins.Left)
                Dim action As PdfLinkAnnotation = New PdfLinkAnnotation(tocPage, titleBounds, New PdfGoToAction(Dest))
                action.Border.Width = 0
                PdfAnnotationCollection.Create(tocPage).Add(action)
                y += titleSize.Height + 10
            Next

            'Save the result pdf document
            doc.SaveToFile("AddTableOfContents.pdf")
            doc.Close()
        End Sub
    End Class
End Namespace