Highlight selected word in MS Word document

In my application I select word in document, then I click on button and I want to highlight this word. It works but when I have word followed by comma or dot, for example ' hello, ', in docRange.Text is only character comma (without word 'hello').

What I am doing wrong?

Words doc; 
doc=Globals.ThisAddIn.Application.Selection.Words;

foreach (Range docRange in doc)
{      
  docRange.HighlightColorIndex = WdColorIndex.wdYellow;
}