test.cs

string sCDAData = System.IO.File.ReadAllText("004bb033-b948-4f4c-b5bf-a8dbd7d8dd40.xml");

TXTextControl.EmbeddedFile cdaAttachment = 
    new TXTextControl.EmbeddedFile(
        "004bb033-b948-4f4c-b5bf-a8dbd7d8dd40.xml",
        sCDAData,
        null) {
        Description = "CDA2 information",
        Relationship = "Unspecified"
    };

// add the attachment
textControl1.DocumentSettings.EmbeddedFiles = 
    new TXTextControl.EmbeddedFile[] { cdaAttachment };
    
X509Certificate2 cert = new X509Certificate2
    ("textcontrolself.pfx"),
     "yourpassword");

// add the digital signature
TXTextControl.SaveSettings saveSettings = new TXTextControl.SaveSettings()
{
    DigitalSignature = new TXTextControl.DigitalSignature(cert, null)
};

textControl1.Save("cover_letter.pdf", TXTextControl.StreamType.AdobePDFA, saveSettings);