I accidentally overwrote a .docx file with another .docx file on a USB drive. Is there any way I can get the original back?
In theory it is possible to restore files that have been deleted, because often the information is not actually removed, only the reference is deleted.
Wondershare Data Recovery claims file restoration for removable storage devices and other sources. I have not used the program, but it is an example of what you could use.
The success of using data recovery programs depends on the conditions of how the file was deleted, how much the drive was used afterwards, etc.
Since you stated that you "overwrote" one .docx with another .docx, then that write most likely already erased the original information. But to be sure you may want to try some data restore software.