How to add semitransparent text watermarks to existing PDF document using Bytescout.PDF library for .NET

using System;
using System.Collections.Generic;
using System.Text;
using Bytescout.PDF;
using System.Diagnostics;

namespace HelloWorld
{
class Program
{
static void Main(string[] args)
{
// Create main PDF Doc Engine
PDFDocEngine engine = new PDFDocEngine("", "");

// Add new document
Document document = engine.AddDocument("Document.pdf");

for (uint i = 0; i < 4; i++)
{
// Append new page to the document
Page page = document.GetPage(i);

// Create new drawing
Drawing drawing = page.AddDrawing();

// Add standard font
uint font = document.AddFontStandard(StandardFontType.TimesBold, FontEncodingType.WinAnsi);

// Set Active Font
drawing.SetActiveFont(font, 200, false, false);

// Set output text
string txt = "Page " + (i+1).ToString();

// Set text color
drawing.SetColor(Drawing.RGBToColor(255, 0, 0));

// Save the current graphics state on the graphics state stack
drawing.StateStore();

// Create new graphic state
DrawingState drawingState = new DrawingState(document);

// Set fill alpha blending to 30%
drawingState.AlphaFill = 0.3f;
// Set lines alpha blending to 100%
drawingState.AlphaStroke = 1.0f;
// Set graphic state as current
drawing.SetGState(drawingState);

// Place Text
drawing.PlaceText(100.0f, 600.0f, 45.0f, txt);

// Restore previous graphics state
drawing.StateRestore();

// Closing drawing on the page
drawing.Close();
}
// Save document
document.Save("Result.pdf");

// open generated PDF document in default PDF viewer installed in Windows
Process.Start("Result.pdf");
}
}
}

Download example source code: bytescoutpdf_watermarking_pdf_documents.zip (40 KB)