public void InsertMathMl()
{
Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);
const string MathMl = "<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>a</mi><mrow><mn>1</mn></mrow></msub><mo>+</mo><msub><mi>b</mi><mrow><mn>1</mn></mrow></msub></mrow></math>";
builder.InsertHtml(MathMl);
doc.Save(MyDir + "MathML.docx");
doc.Save(MyDir + "MathML.pdf");
}