Check Tools/Options/Save if the "Always create backup copy" checkbox is
ticked you may be in luck. If it's not checked then you'll need to recreate
the document.
If the checkbox is ticked look in the folder that you saved you file to and
look for a filename that says "Backup of" whatever your file name is ".wbk".
So if your original file was called "My Work.doc" the backup file will be
called "Backup of My Work.wbk".
If the file exists, open the backup file from within Word and use the SaveAs
command to save the file with its original filename.
Thanks for the suggestion - unfortunately it was not checked - boy did I learn a big lesson on this one - and you would think after years of using Word I would know better. Sigh......
It's probably too late now, but a reminder for next time: If you discover
the mistake before you close the document, even after saving, you can click
Undo and get back everything you deleted. Once you close the document,
though, it's gone.