How do I recover a document I overwrote in Word?

[Peachy]

Instead of hitting "Save As" I hit the "Save" button. How do I get the old
document back?

 

[Charles Kenyon]

You don't unless you have a backup. Word provides for making such a backup
but you have to turn the option on.
Tools > Options > Save (tab)
Check the option to always save a backup copy.
Note there is _one_ backup copy per document so if you save twice, you wipe
out the old backup with the new one.

 

[Suzanne S. Barnhill]

If the document is still open, you can Undo back to the point where you
started, resave, then Redo all the actions and Save As. If you have closed
the document but have "Automatically create backup copy," you can find your
previous version as "Backup of <filename>.wbk" in the document folder.