PM> Install-Package Spire.Doc

using Spire.Doc;
using Spire.Doc.Documents;

namespace ConvertHtmlToPdf
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Create an instance of the Document class
            Document doc = new Document();
            // Load an HTML file
            doc.LoadFromFile("Sample.html", FileFormat.Html, XHTMLValidationType.None);

            //Convert the HTML file to PDF format
            doc.SaveToFile("HtmlToPDF.pdf", FileFormat.PDF);
            doc.Close();
        }
    }
}

using Spire.Doc;
using Spire.Doc.Documents;

namespace ConvertHtmlStringToPdf
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Create an instance of the Document class
            Document doc = new Document();
            // Add a paragraph to the document
            Paragraph para = doc.AddSection().AddParagraph();
            // Specify the HTML string
            string htmlString = @"<h1>This is a Heading</h1>
                                  <p>This is a paragraph.</p>
                                  <ul>
                                    <li>Item 1</li>
                                    <li>Item 2</li>
                                    <li>Item 3</li>
                                  </ul>";

            // Append the HTML string to the paragraph
            para.AppendHTML(htmlString);

            // Convert the document to PDF format
            doc.SaveToFile("HtmlStringToPDF.pdf", FileFormat.PDF);
            doc.Close();
        }
    }
}

using Spire.Doc;
using Spire.Doc.Documents;

namespace ConvertHtmlToXps
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Create an instance of the Document class
            Document doc = new Document();
            // Load an HTML file
            doc.LoadFromFile("Sample.html", FileFormat.Html, XHTMLValidationType.None);

            //Convert the HTML file to XPS format
            doc.SaveToFile("HtmlToXPS.xps", FileFormat.XPS);
            doc.Close();
        }
    }
}

using Spire.Doc;
using Spire.Doc.Documents;

namespace ConvertHtmlToXml
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Create an instance of the Document class
            Document doc = new Document();
            // Load an HTML file
            doc.LoadFromFile("Sample.html", FileFormat.Html, XHTMLValidationType.None);

            //Convert the HTML file to XML format
            doc.SaveToFile("HtmlToXML.xml", FileFormat.Xml);
            doc.Close();
        }
    }
}

PM> Install-Package Spire.PDF

using Spire.Pdf.Annotations;
using Spire.Pdf;
using Spire.Pdf.Texts;
using System.Drawing;

namespace AddMarkupAnnotation
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            // Load a PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Terms of service.pdf");

            // Get a specific page
            PdfPageBase page = doc.Pages[0];

            // Create a PdfTextFinder object based on the page
            PdfTextFinder finder = new PdfTextFinder(page);

            // Set the find options
            finder.Options.Parameter = TextFindParameter.WholeWord;
            finder.Options.Parameter = TextFindParameter.IgnoreCase;

            // Find the instances of the specified text
            List<PdfTextFragment> fragments = finder.Find("In order to help make the Site a secure environment" +
                " for the purchase and sale of Marketplace Offerings, all users are required to accept and " +
                "comply with these Terms of Service.");

            // Get the first instance
            PdfTextFragment textFragment = fragments[0];

            // Specify annotation text
            String text = "There is a markup annotation added by Spire.PDF for .NET.";

            // Iterate through the bounds of the found text
            for (int i = 0; i < textFragment.Bounds.Length; i++)
            {
                // Get a specific bound
                RectangleF rect = textFragment.Bounds[i];

                // Create a text markup annotation
                PdfTextMarkupAnnotation annotation = new PdfTextMarkupAnnotation("Administrator", text, rect);

                // Set the markup color
                annotation.TextMarkupColor = Color.Green;

                // Add the annotation to the collection of the annotations
                page.Annotations.Add(annotation);
            }

            // Save result to file
            doc.SaveToFile("AddMarkups.pdf");

            // Dispose resources
            doc.Dispose();
        }
    }
}

using Spire.Pdf.Annotations;
using Spire.Pdf.Texts;
using Spire.Pdf;
using Spire.Pdf.Graphics;
using System.Drawing;

namespace AddFreeTextAnnotation
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            // Load a PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Terms of service.pdf");

            // Get a specific page
            PdfPageBase page = doc.Pages[0];

            // Create a PdfTextFinder object based on the page
            PdfTextFinder finder = new PdfTextFinder(page);

            // Set the find options
            finder.Options.Parameter = TextFindParameter.WholeWord;
            finder.Options.Parameter = TextFindParameter.IgnoreCase;

            // Find the instances of the specified text
            List<PdfTextFragment> fragments = finder.Find("Marketplace Offerings");

            // Get the first instance
            PdfTextFragment textFragment = fragments[0];

            // Get the text bound
            RectangleF rect = textFragment.Bounds[0];

            // Get the x and y coordinates to add annotation
            float x = rect.Right;
            float y = rect.Bottom;

            // Create a free text annotation
            RectangleF rectangle = new RectangleF(x, y, 130, 30);
            PdfFreeTextAnnotation textAnnotation = new PdfFreeTextAnnotation(rectangle);

            // Set the content of the annotation
            textAnnotation.Text = "There is a free text annotation\radded by Spire.PDF for .NET.";

            // Set other properties of annotation
            PdfFont font = new PdfFont(PdfFontFamily.TimesRoman, 10f, PdfFontStyle.Bold);
            PdfAnnotationBorder border = new PdfAnnotationBorder(1f);
            textAnnotation.Font = font;
            textAnnotation.Border = border;
            textAnnotation.BorderColor = Color.Purple;
            textAnnotation.Color = Color.Green;
            textAnnotation.Opacity = 1.0f;

            // Add the annotation to the collection of the annotations
            page.Annotations.Add(textAnnotation);

            // Save result to file
            doc.SaveToFile("FreeTextAnnotation.pdf");

            // Dispose resources
            doc.Dispose();
        }
    }
}

using Spire.Pdf.Annotations;
using Spire.Pdf.Texts;
using Spire.Pdf;
using System.Drawing;

namespace AddPopupAnnotation
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            // Load a PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Terms of service.pdf");

            // Get a specific page
            PdfPageBase page = doc.Pages[0];

            // Create a PdfTextFinder object based on the page
            PdfTextFinder finder = new PdfTextFinder(page);

            // Set the find options
            finder.Options.Parameter = TextFindParameter.WholeWord;
            finder.Options.Parameter = TextFindParameter.IgnoreCase;

            // Find the instances of the specified text
            List<PdfTextFragment> fragments = finder.Find("Marketplace Offerings");

            // Get the first instance
            PdfTextFragment textFragment = fragments[0];

            // Get the text bound
            RectangleF textBound = textFragment.Bounds[0];

            // Get the x and y coordinates to add annotation
            float x = textBound.Right + 5;
            float y = textBound.Top - 15;

            // Create a popup annotation
            RectangleF rectangle = new RectangleF(x, y, 30, 30);
            PdfPopupAnnotation popupAnnotation = new PdfPopupAnnotation(rectangle);
            
            // Set the annotation text
            popupAnnotation.Text = "There is a popup annotation\radded by Spire.PDF for .NET.";

            // Set the icon and color of the annotation
            popupAnnotation.Icon = PdfPopupIcon.Comment;
            popupAnnotation.Color = Color.Red;

            // Add the annotation to the collection of the annotations
            page.Annotations.Add(popupAnnotation);

            // Save result to file
            doc.SaveToFile("PopupAnnotation.pdf");

            // Dispose resources
            doc.Dispose();
        }
    }
}

using Spire.Pdf.Annotations;
using Spire.Pdf.Texts;
using Spire.Pdf;
using System.Drawing;

namespace AddShapeAnnotation
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            // Load a PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Terms of service.pdf");

            // Get a specific page
            PdfPageBase page = doc.Pages[0];

            // Create a PdfTextFinder object based on the page
            PdfTextFinder finder = new PdfTextFinder(page);

            // Set the find options
            finder.Options.Parameter = TextFindParameter.WholeWord;
            finder.Options.Parameter = TextFindParameter.IgnoreCase;

            // Find the instances of the specified text
            List<PdfTextFragment> fragments = finder.Find("Marketplace Offerings");

            // Get the first instance
            PdfTextFragment textFragment = fragments[0];

            // Get the text bound
            RectangleF textBound = textFragment.Bounds[0];

            // Get the coordinates to add annotation
            float left = textBound.Left;
            float top = textBound.Top;
            float right = textBound.Right;
            float bottom = textBound.Bottom;

            // Create a shape nnotation
            PdfPolyLineAnnotation polyLineAnnotation = new PdfPolyLineAnnotation(page, new PointF[] { 
                new PointF(left, top), new PointF(right, top), new PointF(right - 5, bottom), new PointF(left - 5, bottom), new PointF(left, top) });

            // Set the annotation text
            polyLineAnnotation.Text = "There is a shape annotation\radded by Spire.PDF for .NET.";

            // Add the annotation to the collection of the annotations
            page.Annotations.Add(polyLineAnnotation);

            // Save result to file
            doc.SaveToFile("ShapeAnnotation.pdf");

            // Dispose resources
            doc.Dispose();
        }
    }
}

using Spire.Pdf.Annotations;
using Spire.Pdf.Texts;
using Spire.Pdf;
using System.Drawing;

namespace AddUrlAnnotation
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            // Load a PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Terms of service.pdf");

            // Get a specific page
            PdfPageBase page = doc.Pages[0];

            // Create a PdfTextFinder object based on the page
            PdfTextFinder finder = new PdfTextFinder(page);

            // Set the find options
            finder.Options.Parameter = TextFindParameter.WholeWord;
            finder.Options.Parameter = TextFindParameter.IgnoreCase;

            // Find the instances of the specified text
            List<PdfTextFragment> fragments = finder.Find("Marketplace Offerings");

            // Get the first instance
            PdfTextFragment textFragment = fragments[0];

            // Get the text bound
            RectangleF textBound = textFragment.Bounds[0];

            // Create a Url annotation
            PdfUriAnnotation urlAnnotation = new PdfUriAnnotation(textBound, "https://www.e-iceblue.com/");

            // Add the annotation to the collection of the annotations
            page.Annotations.Add(urlAnnotation);

            // Save result to file
            doc.SaveToFile("UrlAnnotation.pdf");

            // Dispose resources
            doc.Dispose();
        }
    }
}

using Spire.Pdf.Annotations;
using Spire.Pdf.Texts;
using Spire.Pdf;
using System.Drawing;

namespace AddFileLinkAnnotation
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            // Load a PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Terms of service.pdf");

            // Get a specific page
            PdfPageBase page = doc.Pages[0];

            // Create a PdfTextFinder object based on the page
            PdfTextFinder finder = new PdfTextFinder(page);

            // Set the find options
            finder.Options.Parameter = TextFindParameter.WholeWord;
            finder.Options.Parameter = TextFindParameter.IgnoreCase;

            // Find the instances of the specified text
            List<PdfTextFragment> fragments = finder.Find("Marketplace Offerings");

            // Get the first instance
            PdfTextFragment textFragment = fragments[0];

            // Get the text bound
            RectangleF textBound = textFragment.Bounds[0];

            // Create a file link annotation
            PdfFileLinkAnnotation fileLinkAnnotation = new PdfFileLinkAnnotation(textBound, "C:\\Users\\Administrator\\Desktop\\Report.docx");

            // Add the annotation to the collection of the annotations
            page.Annotations.Add(fileLinkAnnotation);

            // Save result to file
            doc.SaveToFile("FileLinkAnnotation.pdf");

            // Dispose resources
            doc.Dispose();
        }
    }
}

using Spire.Pdf.Annotations;
using Spire.Pdf.Texts;
using Spire.Pdf;
using Spire.Pdf.General;
using System.Drawing;

namespace AddDocumentLinkAnnotation
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a PdfDocument object
            PdfDocument doc = new PdfDocument();

            // Load a PDF file
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Terms of service.pdf");

            // Get a specific page
            PdfPageBase page = doc.Pages[0];

            // Create a PdfTextFinder object based on the page
            PdfTextFinder finder = new PdfTextFinder(page);

            // Set the find options
            finder.Options.Parameter = TextFindParameter.WholeWord;
            finder.Options.Parameter = TextFindParameter.IgnoreCase;

            // Find the instances of the specified text
            List<PdfTextFragment> fragments = finder.Find("Marketplace Offerings");

            // Get the first instance
            PdfTextFragment textFragment = fragments[0];

            // Get the text bound
            RectangleF textBound = textFragment.Bounds[0];

            // Create a document link annotation
            PdfDocumentLinkAnnotation documentLinkAnnotation = new PdfDocumentLinkAnnotation(textBound);
     
            // Set the destination of the annotation
            documentLinkAnnotation.Destination = new PdfDestination(doc.Pages[1]);

            // Add the annotation to the collection of the annotations
            page.Annotations.Add(documentLinkAnnotation);

            // Save result to file
            doc.SaveToFile("DocumentLinkAnnotation.pdf");

            // Dispose resources
            doc.Dispose();
        }
    }
}