public static void AddWatermarkToFirstPage()
{
  Console.WriteLine( "=== ADD WATERMARKS TO FIRST PAGE ===" );
  var outputFileName = "AddWatermarkToFirstPage.pdf";
  var outputPath = WatermarksSample.WatermarksSampleOutputDirectory + outputFileName;

  // Create a pdf document.
  using( var pdfoutput = PdfDocument.Create( outputPath ) )
  {
    // Get the first page of the document.
    var page = pdfoutput.Pages.First();

    // Add title.
    var textStyle = TextStyle.WithFont( pdfoutput.Fonts.GetStandardFont( StandardFontType.Helvetica ), 15d );
    page.AddParagraph( "Add Watermarks to first page only", textStyle, new ParagraphStyle( ParagraphHorizontalAlignment.Center ) );

    // Add Text to first page.
    page.AddText( "This is the first page of the document", new Point( 100, 100 ) );

    // Add a second page and add text to it.
    page = pdfoutput.Pages.Add();
    page.AddParagraph( "This is the second page of the document" );

    // Define a watermark using the default watermark TextStyle and add it only for first page.
    var watermark = new Watermark( "Confidential" );
    pdfoutput.Pages[ 0 ].Watermarks.Add( watermark );

    // Save the output document.
    pdfoutput.Save();
    Console.WriteLine( $"Info exported to path: {outputFileName}" );
  }
}

public static void AddWatermarksToAllPages()
{
  Console.WriteLine( "=== ADD WATERMARKS TO ALL PAGES ===" );
  var outputFileName = "AddWatermarkToAllPages.pdf";
  var outputPath = WatermarksSample.WatermarksSampleOutputDirectory + outputFileName;

  // Create a pdf document.
  using( var pdfoutput = PdfDocument.Create( outputPath ) )
  {
    // Get the first page of the document.
    var page = pdfoutput.Pages.First();

    // Add title.
    var textStyle = TextStyle.WithFont( pdfoutput.Fonts.GetStandardFont( StandardFontType.Helvetica ), 15d );
    page.AddParagraph( "Add Watermarks for all pages", textStyle, new ParagraphStyle( ParagraphHorizontalAlignment.Center ) );

    // Add Text to first page.
    page.AddText( "This is the first page of the document", new Point( 100, 100 ) );

    // Add a second page and add text to it.
    page = pdfoutput.Pages.Add();
    page.AddParagraph( "This is the second page of the document" );

    // Define a watermark and add it for all pages.
    var watermarkTextStyle = TextStyle.WithFontAndColor( pdfoutput.Fonts.GetStandardFont( StandardFontType.HelveticaBold ), 300d, Color.Red );
    var watermark = new Watermark( "Big", watermarkTextStyle );
    pdfoutput.Watermarks.Add( watermark );

    // Save the output document.
    pdfoutput.Save();
    Console.WriteLine( $"Info exported to path: {outputFileName}" );
  }
}