Type or Namespace name 'HTMLWorker' could not be found

Type or Namespace name 'HTMLWorker' could not be found

I am using iTextSharp version 4.1.6 in my application. My using includes
both itextsharp.text and itextsharp.text.pdf. I am trying to follow
guidance from stackoverflow on creating a PDF from an html page. This
requires that I use an itextsharp object called HTMLWorker. However the
intellisence shows no such class. When I manually type in "HTMLWorker
worker = new HTMLWorker(doc);" I get an error "Type or Namespace name
'HTMLWorker' could not be found. Are you missing a using directive or a
reference?" Can anyone identify which using or reference I am missing?