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"
    };

textControl1.DocumentSettings.EmbeddedFiles = 
    new TXTextControl.EmbeddedFile[] { cdaAttachment };

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