test.cs

private InvoiceDescriptor ImportZUGFeRD(string filename) {

  // temporary ServerTextControl to load PDF
  using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) {
    tx.Create();

    TXTextControl.LoadSettings ls = new TXTextControl.LoadSettings() {
      PDFImportSettings = TXTextControl.PDFImportSettings.LoadEmbeddedFiles
    };

    // load the embedded file into LoadSettings
    tx.Load(filename, TXTextControl.StreamType.AdobePDF, ls);

    // convert the byte[] to a MemoryStream
    byte[] byteArray = (byte[])ls.EmbeddedFiles[0].Data;
    MemoryStream stream = new MemoryStream(byteArray);

    // return the invoice object structure
    return InvoiceDescriptor.Load(stream);
  }
}