test.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("Arial", 13)};

// Add a signature box to the document
var fieldName = SignatureBoxManager.AddSignatureBox(
    textControl1,
    new Size(8000, 2000),
    1,
    SignatureLocation.BottomLeft,
    signerData,
    signatureStyle
);

// Create a digital signature using a certificate
var certificate = new X509Certificate2("textcontrolself.pfx", "123");
var signatureFields = new List<DigitalSignature> { new DigitalSignature(certificate, null, fieldName) };

var saveSettings = new TXTextControl.SaveSettings
{
    SignatureFields = signatureFields.ToArray()
};

// Save the document as PDF/A
textControl1.Save("signed.pdf", TXTextControl.StreamType.AdobePDFA, saveSettings);