Excel 2007 (2003 .xls format)

I just opened a spreadsheet and on doing so I am not sure it is the one that
I want. I could tell this by the date it was modified last. Upon looking
with Windows Explorer under the "Date modified" column it gives today's
date! It is not giving the date of last modification but the date of last
opening.

How can I find this out please. It is very important.

Thanks in advance... Bob