How to apply transparent background to barcode using C# and VB.NET in WinForms PDF?

using Syncfusion.Pdf.Barcode;
using System.Drawing;
using System.IO;

Imports Syncfusion.Pdf.Barcode
Imports System.Drawing
Imports System.IO

//Create a bitmap.  
Bitmap bmp = new Bitmap(200, 200);
 
//Create graphics from the bitmap.   
Graphics graphics = Graphics.FromImage(bmp);
 
//Drawing QR Barcode.  
PdfQRBarcode barcode = new PdfQRBarcode();
 
//Set the Error correction level.  
barcode.ErrorCorrectionLevel = PdfErrorCorrectionLevel.High;
 
//Creates a new PdfBarcodeQuietZones.
PdfBarcodeQuietZones quietZones = new PdfBarcodeQuietZones();
quietZones.All = 0f;
 
//Set the XDimension.  
barcode.XDimension = 3;
 
//Add the barcode text.
barcode.Text = "http://www.syncfusion.com";
 
//Apply the quiet zone. 
barcode.QuietZone = quietZones;
 
//Convert the barcode to an image.  
System.Drawing.Image barcodeImage = barcode.ToImage();
 
//Set transparency to the image.     
Bitmap bitmap = (Bitmap)barcodeImage;
bitmap.MakeTransparent(System.Drawing.Color.Transparent);
 
//Save the transparency applied image. 
MemoryStream imageStream = new MemoryStream();
bitmap.Save(imageStream, System.Drawing.Imaging.ImageFormat.Png);
 
//Load the transparency applied image.  
System.Drawing.Image transparencyImage = System.Drawing.Image.FromStream(imageStream);
 
//Fill the rectangle with transparency.   
Brush brush = new SolidBrush(System.Drawing.Color.FromArgb(128, 128, 128, 128));
graphics.FillRectangle(brush, 0, 0, 200, 200);
 
//Draw the transparency image with the bitmap graphics. 
graphics.DrawImage(transparencyImage, new System.Drawing.RectangleF(0, 0, 200, 200));
 
//Save the transparency image.  
bmp.Save("Barcode.png", System.Drawing.Imaging.ImageFormat.Png);
 
//Dispose all the objects. 
graphics.Dispose();
bmp.Dispose();
bitmap.Dispose();

'Create a bitmap.  
Dim bmp As Bitmap = New Bitmap(200, 200)
 
'Create graphics from the bitmap.    
Dim graphics As Graphics = Graphics.FromImage(bmp)
 
'Drawing QR Barcode.  
Dim barcode As PdfQRBarcode = New PdfQRBarcode()
 
'Set the Error correction level.   
barcode.ErrorCorrectionLevel = PdfErrorCorrectionLevel.High
 
'Creates a new PdfBarcodeQuietZones. 
Dim quietZones As PdfBarcodeQuietZones = New PdfBarcodeQuietZones()
quietZones.All = 0F
 
'Set the XDimension.   
barcode.XDimension = 3
 
'Add the barcode text.
barcode.Text = "http://www.syncfusion.com"
 
'Apply the quiet zone. 
barcode.QuietZone = quietZones
 
'Convert the barcode to an image  
Dim barcodeImage As System.Drawing.Image = barcode.ToImage()
 
'Set transparency to the image      
Dim bitmap As Bitmap = CType(barcodeImage, Bitmap)
bitmap.MakeTransparent(System.Drawing.Color.Transparent)
 
'Save the transparency applied image. 
Dim imageStream As MemoryStream = New MemoryStream()
bitmap.Save(imageStream, System.Drawing.Imaging.ImageFormat.Png)
 
'Load the transparency applied image.   
Dim transparencyImage As System.Drawing.Image = System.Drawing.Image.FromStream(imageStream)
 
'Fill the rectangle with transparency.    
Dim brush As Brush = New SolidBrush(System.Drawing.Color.FromArgb(128, 128, 128, 128))
graphics.FillRectangle(brush, 0, 0, 200, 200)
 
'Draw the transparency image with the bitmap graphics. 
graphics.DrawImage(transparencyImage, New System.Drawing.RectangleF(0, 0, 200, 200))
 
'Save the transparency bitmap.   
bmp.Save("Barcode.png", System.Drawing.Imaging.ImageFormat.Png)
 
//Dispose all the objects. 
graphics.Dispose()
bmp.Dispose()
bitmap.Dispose()