custom.cs

var signerData = new SignerData(
    "John Doe", "Signer", "676 Sign Street", "john@signer.com", "I approve this document");

var signatureStyle = new SignatureStyle { 
    SvgImage = System.IO.File.ReadAllText("signature.svg"),
        DetailsFont = new Font("Times New Roman", 13)};

// Add a signature box to the document
var fieldName = SignatureBoxManager.AddSignatureBox(
    textControl1,
    new Size(3000, 2000),
    1,
    SignatureLocation.TopRight,
    signerData,
    signatureStyle
);