In this particular case I have used following workaround to find out if text was found or not:
IMarkupPointer pBegin, pEnd;
IMarkupServices markupServices;
// ...
pBegin.findText(word, 2, pEnd, null);
IHTMLTxtRange range = htmlDocument2.selection.createRange();
markupServices.MoveRangeToPointers(pBegin, pEnd, range);
if(range.text != word)
{
// ...Text not found
}