How to create PDF Signature Box using iTextSharp in C-sharp

 I can suggest some popular libraries that might fit your needs:

1. **iTextSharp**: It's a PDF manipulation library that can be used to add digital signatures to PDF documents. You can find it on GitHub: https://github.com/itext/itext7-dotnet

2. **BouncyCastle**: It's a security library that includes cryptographic algorithms and digital signature functionality. You can find it on GitHub: https://github.com/bouncycastle/bouncycastle-dotnet

3. **DotNetOpenAuth**: It's an open-source library for implementing OAuth and OpenID protocols in .NET applications. While it doesn't have a built-in digital signature feature, it can be used to sign requests and responses in the context of OAuth. You can find it on GitHub: https://github.com/dotnetopenauth/DotNetOpenAuth

To use these libraries, you'll need to download them from their respective GitHub pages, install them in your project, and then use their APIs to add digital signatures to your documents or messages. I recommend checking their documentation for more detailed instructions on how to use their signature features.

Here's an example of how to use iTextSharp to add a digital signature to a PDF document:

```csharp
using iText.Kernel.Pdf;
using iText.Signatures;
using iText.Security.Crypto;
using iText.Layout;
using iText.Layout.Element;
using iText.Layout.Properties;
using System;
using System.IO;

class Program
{
    static void Main(string[] args)
    {
        string srcPdf = "input.pdf";
        string destPdf = "output.pdf";

        using (PdfDocument document = new PdfDocument(new PdfWriter(destPdf)))
        {
            PdfDocument srcDoc = new PdfDocument(new FileStream(srcPdf, FileMode.Open, FileAccess.Read));
            document.Add(new CopyPages(srcDoc, new IdentityTransform(1, 1), new Rectangle(1, 1, document.Width - 2 * 10, document.Height - 2 * 10)));

            // Add text and image
            Document doc = new Document(document);
            Paragraph text = new Paragraph("This is the text to be signed.")
                .Add(new Image("logo.png"))
                .SetTextAlignment(TextAlignment.CENTER)
                .SetFontSize(12)
                .SetFontFamily("Arial");
            doc.Add(text);

            // Add signature field
            Document signatureDoc = new Document(document);
            Paragraph signatureText = new Paragraph("Signature:")
                .SetTextAlignment(TextAlignment.LEFT)
                .SetFontSize(12)
                .SetFontFamily("Arial");
            signatureDoc.Add(signatureText);
            Rectangle signatureRect = new Rectangle(100, document.Height - 50, 150, 30);
            signatureDoc.Add(new SignatureField("sig")
                .SetRectangle(signatureRect)
                .SetReason("Reason for signing")
                .SetFlags(MakeSignatureFlags.SubFilterUsageAdobeAcroForms20 | MakeSignatureFlags.Visible | MakeSignatureFlags.DoNotStore));

            // Add signature to the document
            PdfSignatureAppearance appearance = document.AddSignature(signatureRect, "sig", new StampingProperties());
            appearance.SetReason("Reason for signing");
            appearance.SetLocation("Location for signing");
            appearance.SetSignDate("2023-03-15T14:30:00Z");
            appearance.SetVisibleSignature(new Rectangle(100, document.Height - 70, 150, 30), "sig");
            appearance.SetSignatureGraphic(signatureDoc.GetFirstParagraph().GetImage());
            appearance.SetSignatureAppearance(signatureDoc.GetFirstParagraph().GetImage().GetUnderlyingStream());
            appearance.SetSigningDate("2023-