I worked on a Word document and also saved the file on my flash drive. When it asked me to save, I pressed the
Replace document option by mistake.
I can see the missing work under the
Properties menu. Will I be able to recover the lost work?
It depends on the Operating System. If you're running a newer version of Windows, right clicking the file will reveal "previous versions," and you should be able to roll back the document to that. If you had track changes enabled, you could always restore there too.
Another option might be to use file recovery, though it doesn't always work. You may try to use http://www.piriform.com/recuva from windows or testdisk from GNU/Linux or a LiveCD. Or simply google for "free file recovery" and you'll get a long list of programs designed to recover accidentaly deleted files. Since here you didn't delete but overwrite the file it may also not work, but since the file got overwrited by something very different it may also show up as another version in the recovery program. All lies whethever the overwrite process affects the same physical sectors as the original's file and / or how many traces it leaves there.
Otherwise nicatronTg's answer may be the best bet, though it seems to me that "previous versions" is not enabled by default.