I am working on a document which suddenly was closed and disappeared and cannot find it.
I did not save it before.
Sorry to hear about your experience.
If you have saved a copy of the file or uploaded it to the cloud, then you can give it a try to recover from there.
If the document was abruptly closed and nothing saved, then sorry to say there isn't much that can be done from our end.
Also, keep this setting enabled for the future to avoid losing data:
Acrobat Reader>Edit>Preferences>Documents> automatically save document changes...>OK
Check the Recent Files list, under the File menu. Does it appear there? If so, click it to open it.