How to convert a simple PDF to PDF a/3 format with XML file embedded

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C#6.0

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Hi All,
I need a solution for converting a simple PDF to PDF A/3 format with xml file embedded by adding an image or icon before converting to a/3 format with any open source. Please help

Thanks in advance

What I have tried:

byte[] doc_bytes_invoice_added = null;
                string input = @"C':\test\";
                using (PDFDoc in_doc = new PDFDoc(input + "output.pdf"))
                {
                    in_doc.InitSecurityHandler();
                    NameTree files = NameTree.Create(in_doc, "EmbeddedFiles");
                    FileSpec fs = FileSpec.Create(in_doc, input + "ZUGFeRD-invoice.xml", true);
                    byte[] file1_name = System.Text.Encoding.UTF8.GetBytes("ZUGFeRD-invoice.xml");
                    files.Put(file1_name, fs.GetSDFObj());
                    fs.GetSDFObj().PutText("Desc", "ZUGFeRD Rechnung");
                    fs.GetSDFObj().PutName("AFRelationship", "Alternative");
                    fs.GetSDFObj().PutText("F", "ZUGFeRD-invoice.xml");
                    fs.GetSDFObj().PutText("UF", "ZUGFeRD-invoice.xml");
                    Obj collection = in_doc.GetRoot().FindObj("Collection");
                    if (collection == null) collection = in_doc.GetRoot().PutDict("Collection");
                    collection.PutName("View", "T");
                    doc_bytes_invoice_added = in_doc.Save(SDFDoc.SaveOptions.e_incremental);
                }