For HTML2PDF and XML2PDF solution check our PDFDoc Scout ActiveX library instead

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();

// Append new page to the document
Page page = document.AddPage(PageSizeType.A3, PageOrientationType.LandScape);

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

// Line width
const double lineWidth = 3.0f;

// Set Line Width
drawing.SetLineWidth(lineWidth);

// 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);

// Create yellow fill color
Color yellowColor = Drawing.RGBToColor(255, 218, 11);

// Set fill color
drawing.SetFillColor(yellowColor);

// Draw rectangle
drawing.rectangle(100.0f, 100.0f, 400.0f, 400.0f);

// Fill and stroke rectangle
drawing.FillAndStroke();

// Restore the current graphics state from the graphics state stack
drawing.StateRestore();

drawing.StateStore();

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

// Set alpha blending to shapes
drawingState.AlphaIsShape = true;
// Set fill alpha blending to 70%
drawingState.AlphaFill = 0.7f;
// Set lines alpha blending to 100%
drawingState.AlphaStroke = 1.0f;

// Set graphic state as current
drawing.SetGState(drawingState);

// Create green fill color
Color greenColor = Drawing.RGBToColor(30, 131, 35);

// Set fill color
drawing.SetFillColor(greenColor);

// Create new path
drawing.NewPath();
// Draw from point with coordinate (200, 200)...
drawing.MoveTo(200.0f, 200.0f);
// ... to point with coordinate (200, 600) and then ...
drawing.LineTo(200.0f, 600.0f);
// ... to point with coordinate (600, 600) and then ...
drawing.LineTo(600.0f, 600.0f);
// ... to point with coordinate (600, 200).
drawing.LineTo(600.0f, 200.0f);
// Close new path
drawing.ClosePath();

// Fill shape
drawing.Fill();

// Restore the current graphics state from the graphics state stack
drawing.StateRestore();

// Closing drawing on the page
drawing.Close();

// Save document
document.Save("AlphaBlending.pdf");

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

Download example source code: bytescoutpdf/bytescoutpdf_transparent_drawings.zip (4 KB)

For HTML2PDF and XML2PDF solution check our PDFDoc Scout ActiveX library instead