Convert form control of docx file to html

Question

I'm extract form control of docx like this:

using (var doc = WordprocessingDocument.Open("sampleTest3.docx", false))
{
    foreach (var control in doc.MainDocumentPart.Document.Body.Descendants<SdtElement>())
    {
       //How to convert control to html string
    }
}

and convert docx file to html using https://stackoverflow.com/a/41255515/2699910.
but is there a way to convert just form control as html(not whole file)?