using (Signature signature = new Signature("sample.pdf"))
{
    TextSignOptions options = new TextSignOptions("John Smith")
    {
        // locate signature
        Left = 100, Top = 100, Width = 100, Height = 30,
        // set text color and font
        ForeColor = Color.Red,
        Font = new SignatureFont { Size = 12, FamilyName = "Comic Sans MS" }
    };
    // sign document to file
    signature.Sign("signed.pdf", options);
}