test.cs

[HttpPost]
public bool Create(string document, string name) {

   var snippetName = _applicationSettings.SnippetDirectory +
      "/" + Path.GetInvalidFileNameChars().Aggregate(name, (f, c) => f.Replace(c, '_').Replace(' ', '_'));

   using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) {
      tx.Create();

      // load the snippet
      tx.Load(Convert.FromBase64String(document), TXTextControl.BinaryStreamType.InternalUnicodeFormat);

      // select 200 chars as a preview
      tx.Select(0, 200);

      // save the body of the snippet
      TXTextControl.SaveSettings saveSettings = new TXTextControl.SaveSettings() {
         CssSaveMode = TXTextControl.CssSaveMode.Inline
      };

      tx.Selection.Save(out string htmlString, TXTextControl.StringStreamType.HTMLFormat, saveSettings);

      TextReader reader = new StringReader(htmlString);
      HtmlDocument doc = new HtmlDocument();
      doc.Load(reader);
      HtmlNode bodyNode = doc.DocumentNode.SelectSingleNode("/html/body");
      System.IO.File.WriteAllText(snippetName + ".htm", bodyNode.InnerHtml);
   }

   // store the actual snippet in the Text Control format
   System.IO.File.WriteAllBytes(snippetName + ".tx", Convert.FromBase64String(document));

   return true;
}