test.cs

public static string CreateStyleFromSelection(this TXTextControl.TextControl textControl) {

   // get current input position
   var iParStart = textControl.Paragraphs.GetItem(
      textControl.InputPosition.TextPosition).Start;
   textControl.Select(iParStart, 0);

   // create a new paragraph style based on current formatting
   TXTextControl.ParagraphStyle parStyle = 
      new TXTextControl.ParagraphStyle("custom_" + Guid.NewGuid().ToString());

   // set style
   parStyle.Baseline = textControl.Selection.Baseline;
   parStyle.Bold = textControl.Selection.Bold;
   parStyle.FontName = textControl.Selection.FontName;
   parStyle.FontSize = textControl.Selection.FontSize;
   parStyle.ForeColor = textControl.Selection.ForeColor;
   parStyle.Italic = textControl.Selection.Italic;
   parStyle.Strikeout = textControl.Selection.Strikeout;
   parStyle.TextBackColor = textControl.Selection.TextBackColor;
   parStyle.Underline = textControl.Selection.Underline;

   // add style to TextControl
   textControl.ParagraphStyles.Add(parStyle);

   // return the style name
   return parStyle.Name;
}