You can probably find fragments of it just by using a Hex editor such as WinHex. What you'll want to do is this:
1. Open up notepad (or whatever you used to create the original txt file) and type in a few uncommon words that you know would have been in the lost document.
2. Open of this newly created txt file in a hex editor such as Winhex and take note of how the text appears in hexadecimal code.
3. Open up the thumbdrive using the hex editor and do a search for the hex string of one of those words and see what you find.
Most likely you'll be able to see/read the text right in the hex editor. Just be sure that the view is set to ANSI ACII for the right column.
Here's an example of what a TXT document looks like in Hex:
You'll see I highlighted the word "Editor" which translates to the hex code 45 64 69 74 6F 72 (what you'd want to search to find that word)
If you don't find the text, then it was likely overwritten. Because txt files are very small in size they tend to get saved in the lower LBA regions which is the first to get overwritten after a format.
If you do find the text, you can just highlight the text, save it as a file in the hex editor, add the .txt extension, and it should open up for you.