While responders are trying to be helpful, the issue is that Word provides an NON-MACRO way to put the date/time the document was saved: Insert tab --> Header, click at the location you want the Saved Date, which will show the "Header & Footer Tools" tab,
with the "Design" tab below it. You can then click on the "Document Info" drop-down and select "Field..."
While it may take several steps to get there, it is still much more accessible than diving down into programming macros.
It is already in Word and PowerPoint, which indicates the value of having it.
And I'll add that not having to re-learn how to use the Office members is what makes them "sticky" over open-source alternatives; employers don't have to train (or re-train) employees. What they learn in Word should transfer to Excel, PowerPoint, Publisher
-- you get the idea. This improves productivity for tasks that aren't performed frequently, but a boss may ask his assistant to perform: "Make all my spreadsheets, documents, presentations look uniform, no matter who produced them, INCLUDING WHEN THEY WERE
LAST MODIFIED; I want to know what has changed over time to show our progress."
<sarcasm> Then again, maybe that doesn't matter. </sarcasm>