PDFsharp & MigraDoc Foundation

using PdfSharp.Drawing;
using PdfSharp.Pdf;
using PdfSharp.Pdf.AcroForms;

class SignatureFieldExample
{
    static void Main()
    {
        const string filename = "Output.pdf";

        // Create a new PDF document
        PdfDocument document = new PdfDocument();

        // Add a page to the document
        PdfPage page = document.AddPage();
        XGraphics gfx = XGraphics.FromPdfPage(page);

        // Add a signature field to a specific position
        PdfAcroForm acroForm = document.AcroForm;
        PdfSignatureField signatureField = new PdfSignatureField(page, "SignatureField")
        {
            Left = XUnit.FromCentimeter(5),
            Top = XUnit.FromCentimeter(10),
            Width = XUnit.FromCentimeter(6),
            Height = XUnit.FromCentimeter(2)
        };
        acroForm.Fields.Add(signatureField);

        // Save the document
        document.Save(filename);
    }
}