The sample demonstrates how to sign PDF document with digital certificate.

Download DigitalSignature.pdf

using System;
using System.Drawing;
using Spire.Pdf;
using Spire.Pdf.Graphics;
using Spire.Pdf.Security;

namespace DigitalSignature
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a pdf document.
            PdfNewDocument doc = new PdfNewDocument();

            // Create one page
            PdfPageBase page = doc.Pages.Add();

            //Draw the page
            DrawPage(page);

            String pfxPath = @"Demo.pfx";
            PdfCertificate cert = new PdfCertificate(pfxPath, "e-iceblue");
            PdfSignature signature = new PdfSignature(doc, page, cert, "demo");
            signature.ContactInfo = "Harry Hu";
            signature.Certificated = true;
            signature.DocumentPermissions = PdfCertificationFlags.AllowFormFill;

            //Save pdf file.
            doc.Save("DigitalSignature.pdf");
            doc.Close();

            //Launching the Pdf file.
            System.Diagnostics.Process.Start("DigitalSignature.pdf");
        }

        private static void DrawPage(PdfPageBase page)
        {
            float pageWidth = page.Canvas.ClientSize.Width;
            float y = 0;

            //page header
            PdfPen pen1 = new PdfPen(Color.LightGray, 1f);
            PdfBrush brush1 = new PdfSolidBrush(Color.LightGray);
            PdfTrueTypeFont font1 = new PdfTrueTypeFont(new Font("Arial", 8f, FontStyle.Italic));
            PdfStringFormat format1 = new PdfStringFormat(PdfTextAlignment.Right);
            String text = "Demo of Spire.Pdf";
            page.Canvas.DrawString(text, font1, brush1, pageWidth, y, format1);
            SizeF size = font1.MeasureString(text, format1);
            y = y + size.Height + 1;
            page.Canvas.DrawLine(pen1, 0, y, pageWidth, y);

            //title
            y = y + 5;
            PdfBrush brush2 = new PdfSolidBrush(Color.Black);
            PdfTrueTypeFont font2 = new PdfTrueTypeFont(new Font("Arial", 16f, FontStyle.Bold));
            PdfStringFormat format2 = new PdfStringFormat(PdfTextAlignment.Center);
            format2.CharacterSpacing = 1f;
            text = "Summary of Science";
            page.Canvas.DrawString(text, font2, brush2, pageWidth / 2, y, format2);
            size = font2.MeasureString(text, format2);
            y = y + size.Height + 6;

            //icon
            PdfImage image = PdfImage.FromFile(@"Wikipedia_Science.png");
            page.Canvas.DrawImage(image, new PointF(pageWidth - image.PhysicalDimension.Width, y));
            float imageLeftSpace = pageWidth - image.PhysicalDimension.Width - 2;
            float imageBottom = image.PhysicalDimension.Height + y;

            //refenrence content
            PdfTrueTypeFont font3 = new PdfTrueTypeFont(new Font("Arial", 9f));
            PdfStringFormat format3 = new PdfStringFormat();
            format3.ParagraphIndent = font3.Size * 2;
            format3.MeasureTrailingSpaces = true;
            format3.LineSpacing = font3.Size * 1.5f;
            String text1 = "(All text and picture from ";
            String text2 = "Wikipedia";
            String text3 = ", the free encyclopedia)";
            page.Canvas.DrawString(text1, font3, brush2, 0, y, format3);

            size = font3.MeasureString(text1, format3);
            float x1 = size.Width;
            format3.ParagraphIndent = 0;
            PdfTrueTypeFont font4 = new PdfTrueTypeFont(new Font("Arial", 9f, FontStyle.Underline));
            PdfBrush brush3 = PdfBrushes.Blue;
            page.Canvas.DrawString(text2, font4, brush3, x1, y, format3);
            size = font4.MeasureString(text2, format3);
            x1 = x1 + size.Width;

            page.Canvas.DrawString(text3, font3, brush2, x1, y, format3);
            y = y + size.Height;

            //content
            PdfStringFormat format4 = new PdfStringFormat();
            text = System.IO.File.ReadAllText(@"Summary_of_Science.txt");
            PdfTrueTypeFont font5 = new PdfTrueTypeFont(new Font("Arial", 10f));
            format4.LineSpacing = font5.Size * 1.5f;
            PdfStringLayouter textLayouter = new PdfStringLayouter();
            float imageLeftBlockHeight = imageBottom - y;
            PdfStringLayoutResult result
                = textLayouter.Layout(text, font5, format4, new SizeF(imageLeftSpace, imageLeftBlockHeight));
            if (result.ActualSize.Height < imageBottom - y)
            {
                imageLeftBlockHeight = imageLeftBlockHeight + result.LineHeight;
                result = textLayouter.Layout(text, font5, format4, new SizeF(imageLeftSpace, imageLeftBlockHeight));
            }
            foreach (LineInfo line in result.Lines)
            {
                page.Canvas.DrawString(line.Text, font5, brush2, 0, y, format4);
                y = y + result.LineHeight;
            }
            PdfTextWidget textWidget = new PdfTextWidget(result.Remainder, font5, brush2);
            PdfTextLayout textLayout = new PdfTextLayout();
            textLayout.Break = PdfLayoutBreakType.FitPage;
            textLayout.Layout = PdfLayoutType.Paginate;
            RectangleF bounds = new RectangleF(new PointF(0, y), page.Canvas.ClientSize);
            textWidget.StringFormat = format4;
            textWidget.Draw(page, bounds, textLayout);
        }
    }
}

Imports System.Drawing
Imports Spire.Pdf
Imports Spire.Pdf.Graphics
Imports Spire.Pdf.Security

Namespace DigitalSignature
    Friend Class Program
        Shared Sub Main(ByVal args() As String)
            'Create a pdf document.
            Dim doc As New PdfNewDocument()

            ' Create one page
            Dim page As PdfPageBase = doc.Pages.Add()

            'Draw the page
            DrawPage(page)

            Dim pfxPath As String = "Demo.pfx"
            Dim cert As New PdfCertificate(pfxPath, "e-iceblue")
            Dim signature As New PdfSignature(doc, page, cert, "demo")
            signature.ContactInfo = "Harry Hu"
            signature.Certificated = True
            signature.DocumentPermissions = PdfCertificationFlags.AllowFormFill

            'Save pdf file.
            doc.Save("DigitalSignature.pdf")
            doc.Close()

            'Launching the Pdf file.
            Process.Start("DigitalSignature.pdf")
        End Sub

        Private Shared Sub DrawPage(ByVal page As PdfPageBase)
            Dim pageWidth As Single = page.Canvas.ClientSize.Width
            Dim y As Single = 0

            'page header
            Dim pen1 As New PdfPen(Color.LightGray, 1.0F)
            Dim brush1 As PdfBrush = New PdfSolidBrush(Color.LightGray)
            Dim font1 As New PdfTrueTypeFont(New Font("Arial", 8.0F, FontStyle.Italic))
            Dim format1 As New PdfStringFormat(PdfTextAlignment.Right)
            Dim text As String = "Demo of Spire.Pdf"
            page.Canvas.DrawString(text, font1, brush1, pageWidth, y, format1)
            Dim size As SizeF = font1.MeasureString(text, format1)
            y = y + size.Height + 1
            page.Canvas.DrawLine(pen1, 0, y, pageWidth, y)

            'title
            y = y + 5
            Dim brush2 As PdfBrush = New PdfSolidBrush(Color.Black)
            Dim font2 As New PdfTrueTypeFont(New Font("Arial", 16.0F, FontStyle.Bold))
            Dim format2 As New PdfStringFormat(PdfTextAlignment.Center)
            format2.CharacterSpacing = 1.0F
            text = "Summary of Science"
            page.Canvas.DrawString(text, font2, brush2, pageWidth / 2, y, format2)
            size = font2.MeasureString(text, format2)
            y = y + size.Height + 6

            'icon
            Dim image As PdfImage = PdfImage.FromFile("Wikipedia_Science.png")
            page.Canvas.DrawImage(image, New PointF(pageWidth - image.PhysicalDimension.Width, y))
            Dim imageLeftSpace As Single = pageWidth - image.PhysicalDimension.Width - 2
            Dim imageBottom As Single = image.PhysicalDimension.Height + y

            'refenrence content
            Dim font3 As New PdfTrueTypeFont(New Font("Arial", 9.0F))
            Dim format3 As New PdfStringFormat()
            format3.ParagraphIndent = font3.Size * 2
            format3.MeasureTrailingSpaces = True
            format3.LineSpacing = font3.Size * 1.5F
            Dim text1 As String = "(All text and picture from "
            Dim text2 As String = "Wikipedia"
            Dim text3 As String = ", the free encyclopedia)"
            page.Canvas.DrawString(text1, font3, brush2, 0, y, format3)

            size = font3.MeasureString(text1, format3)
            Dim x1 As Single = size.Width
            format3.ParagraphIndent = 0
            Dim font4 As New PdfTrueTypeFont(New Font("Arial", 9.0F, FontStyle.Underline))
            Dim brush3 As PdfBrush = PdfBrushes.Blue
            page.Canvas.DrawString(text2, font4, brush3, x1, y, format3)
            size = font4.MeasureString(text2, format3)
            x1 = x1 + size.Width

            page.Canvas.DrawString(text3, font3, brush2, x1, y, format3)
            y = y + size.Height

            'content
            Dim format4 As New PdfStringFormat()
            text = System.IO.File.ReadAllText("Summary_of_Science.txt")
            Dim font5 As New PdfTrueTypeFont(New Font("Arial", 10.0F))
            format4.LineSpacing = font5.Size * 1.5F
            Dim textLayouter As New PdfStringLayouter()
            Dim imageLeftBlockHeight As Single = imageBottom - y
            Dim result As PdfStringLayoutResult _
                = textLayouter.Layout(text, font5, format4, New SizeF(imageLeftSpace, imageLeftBlockHeight))
            If result.ActualSize.Height < imageBottom - y Then
                imageLeftBlockHeight = imageLeftBlockHeight + result.LineHeight
                result = textLayouter.Layout(text, font5, format4, New SizeF(imageLeftSpace, imageLeftBlockHeight))
            End If
            For Each line As LineInfo In result.Lines
                page.Canvas.DrawString(line.Text, font5, brush2, 0, y, format4)
                y = y + result.LineHeight
            Next line
            Dim textWidget As New PdfTextWidget(result.Remainder, font5, brush2)
            Dim textLayout As New PdfTextLayout()
            textLayout.Break = PdfLayoutBreakType.FitPage
            textLayout.Layout = PdfLayoutType.Paginate
            Dim bounds As New RectangleF(New PointF(0, y), page.Canvas.ClientSize)
            textWidget.StringFormat = format4
            textWidget.Draw(page, bounds, textLayout)
        End Sub
    End Class
End Namespace