What I want to know is that why after 25 years or so in MS Word when I open a document (usually somebody else's) and close it the app always asks if I want to save the changes even if I just read it and didn't touch anything.
How come MS Word is not able to detect that there were no changes?
Because there's probably something similar to a "Today's Date" field in the document somewhere which will change simply from the act of opening and closing a document.
Sure there must be a technical explanation, yours is very plausible but it doesn't change the fact that this annoyance only happens in MS Word (that I know of); it doesn't happen in MS Excel or OpenOffice Writer for example. If there's a 'today's date' then they can just add an 'last updated date' or similar and keep track of the file changes.
It's more aggravating if we take into account how popular, old and big the application is.
How come MS Word is not able to detect that there were no changes?