How to Add Watermark Annotation to PDF using C#. For more information, please follow link: https://kb.groupdocs.com/annotation/net/how-to-add-watermark-annotation-to-pdf-using-csharp/

How to Add Watermark Annotation to PDF using C#.cs

using System;
using System.Collections.Generic;
using GroupDocs.Annotation;
using GroupDocs.Annotation.Models;
using GroupDocs.Annotation.Models.AnnotationModels;

namespace AddWatermarkAnnotationtoPDFUsingCSharp
{
    internal class Program
    {
        static void Main(string[] args)
        {
            //Set License to avoid the limitations of Annotation library
            License lic = new License();
            lic.SetLicense(@"Conholdate.Annotator.lic");

            //Instantiate Annotator object with input PDF path
            using (Annotator annotator = new Annotator("input.pdf"))
            {
                //Instantiate WatermarkAnnotation object and set it's properties
                WatermarkAnnotation watermark = new WatermarkAnnotation
                {
                    Angle = 75,
                    Box = new Rectangle(200, 200, 100, 50),
                    CreatedOn = DateTime.Now,
                    Text = "Watermark",
                    FontColor = 65535,
                    FontSize = 12,
                    Message = "This is watermark annotation",
                    Opacity = 0.7,
                    AutoScale = true,
                    HorizontalAlignment = HorizontalAlignment.Center,
                    VerticalAlignment = VerticalAlignment.Center,
                    Replies = new List<Reply>
                    {
                        new Reply
                        {
                            Comment = "First comment",
                            RepliedOn = DateTime.Now
                        },
                        new Reply
                        {
                            Comment = "Second comment",
                            RepliedOn = DateTime.Now
                        }
                    }
                };

                //Add Watermark Annotation to PDF
                annotator.Add(watermark);
                //Save the final output PDF
                annotator.Save("result.pdf");
            }
        }
    }
}