Lost or deleted? Backed up?
If lost have you tried searching for a phrase that is in the document? Spotlight should index the content of file as well as the title. CMD plus Space to bring up the Spotlight search window.
If deleted you’ll need to experiment with a file recovery program. Usually these cost money.
If backed up (to Time Machine) then find out how to restore files from Time Machine, it is fairly straightforward. Enter Time Machine from the little menu icon and then navigate to where you think the file is, if you find it right click and Restore