@AdrianHHH Thanks for the info. We will most likely to stick with Excel with both .xls and .xlsx, because that's our business users have always been providing us with before we switched to CodedUI. I will be looking for ways to not only read source files but append/write/update them in run time as we did with UFT before. If you have information about that, it will be very helpful as well.

@PeterMasiar, I have to say that your last comment is just ignorant. Before you made comment like that, have you even tried to google 15 sec to find an answer that cost me days to experiment to make it work?

@FDM Thank you. The working .xlsx Attributes I posted in my answer can be found nowhere. Despite I did search a solution for more than 2 days. MSDN doesn't mention anything about .xlsx format at all.

@PeterMasiar Well, this may not be a real question/solution for people like you who I believe are more experienced and better skilled. However, this is a real question and a real solution for people like me. There are lots of posts out there which failed to work for me.