How to perform WinForms PDF overlay using C# and VB.NET?

This article explains how to perform PDF Overlay using WinForms PDF viewer libraries.

Two PDF documents can be overlayed using Essential® PDF and Essential® PDF viewer libraries. The following steps are involved in overlaying PDF documents.

1. Convert the PDF documents to images with the help of Essential® PDF viewer.
2. Compare the images using open source image Magick library.
3. Save the difference images as PDF document with the help of Essential® PDF.

Steps to overlay the PDF documents programmatically:

1. Create a new Windows Forms application project.

2. Install the Syncfusion.Pdf.WinForms , Syncfusion.PdfViewer.Windows and Magick.NET as reference to your .NET Framework application from NuGet.org.

3. Include the following namespaces in the Form1.Designer.cs file.

   using Syncfusion.Pdf.Parsing;
   using Syncfusion.Pdf.Graphics;
   using Syncfusion.Windows.Forms.PdfViewer;
   using ImageMagick;
   

4. Add a new button in Form1.Designer.cs to overlay two PDF documents as follows.

   private Button button;
   private Label label;
    
   private void InitializeComponent()
   {
       label = new Label();
       button = new Button();
    
       //Label
       label.Location = new System.Drawing.Point(0, 40);
       label.Size = new System.Drawing.Size(426, 35);
       label.Text = "Click the button to view the overlayed  PDF file generated by Essential PDF";
       label.TextAlign = System.Drawing.ContentAlignment.MiddleCenter;
    
       //Button
       button.Location = new System.Drawing.Point(180, 110);
       button.Size = new System.Drawing.Size(85, 26);
       button.Text = "Overlay PDF";
       button.Click += new EventHandler(OverlayPDF);
    
       //Create PDF
       ClientSize = new System.Drawing.Size(450, 150);
       Controls.Add(label);
       Controls.Add(button);
       Text = "Overlay PDF";
   }
   

5. Add the following code in OverlayPDF to compare the PDF files.

   string sourceFile = "../../Data/groundfloor1.pdf";
   //Load the PDF document 
   PdfLoadedDocument loadedDocument = new PdfLoadedDocument(sourceFile);
   //Get the size of page
   SizeF pageSize=loadedDocument.Pages[0].Size;
    
   //Load the first PDF document to compare
   PdfViewerControl pdfViewer = new PdfViewerControl();
   pdfViewer.RenderingEngine = PdfRenderingEngine.Pdfium;
   pdfViewer.ReferencePath = @"../../";
   pdfViewer.Load(sourceFile);
    
   //Load the second PDF document to compare
   PdfViewerControl pdfViewer1 = new PdfViewerControl();
   pdfViewer1.RenderingEngine = PdfRenderingEngine.Pdfium;
   pdfViewer1.ReferencePath = @"../../";
   pdfViewer1.Load("../../Data/groundfloor2.pdf");
    
   //Get the page count
   int pageCount = 0;
   if(pdfViewer.PageCount==pdfViewer1.PageCount)
   {
       pageCount = pdfViewer.PageCount;
   }
    
   for(int i=0;i<pageCount;i++)
   {
       //Export the PDF page to image 
       Bitmap sImage = pdfViewer.ExportAsImage(i);
       Bitmap gImage = pdfViewer1.ExportAsImage(i);
    
       MagickImage image1 = new MagickImage(sImage);
       MagickImage compare = new MagickImage(gImage);
    
       //Generate the diff image
       MagickImage diffImage = new MagickImage();
       double diffPixel = image1.Compare(compare, ErrorMetric.Absolute, diffImage);
       Bitmap differenceImage = diffImage.ToBitmap();
    
       //Replace the page with diff image
       if (diffPixel>0)
       {
           loadedDocument.Pages.RemoveAt(i);
           loadedDocument.Pages.Insert(i, pageSize);
           PdfBitmap image = new PdfBitmap(differenceImage);
           loadedDocument.Pages[i].Graphics.DrawImage(image, 0, 0, loadedDocument.Pages[i].Graphics.ClientSize.Width, loadedDocument.Pages[i].Graphics.ClientSize.Height);
       }
   }
   //Save and close the document
   loadedDocument.Save("OverlayPDF.pdf");
   loadedDocument.Close(true);
    
   //This will open the PDF file so, the result will be seen in default PDF viewer 
   System.Diagnostics.Process.Start("OverlayPDF.pdf");
   

A complete working sample can be download from PDFOverlaySample.zip

By executing the program, you will get the PDF document as follows.