Word Document Disappeared During Copy/Paste

In what application were you performing the Copy and Paste?

An alternative to using Copy and Paste would be to open the document in Word and then use File>Save As to save another copy with a different name.

However, in the File Explorer, there would not normally be any problem with Copying a file that is NOT open in Word and then Pasting it into that folder.  When that is done, " - Copy" will automatically be appended to the filename as shown in the following screen shot of those actions just being performed.

If you provide access to the document that you were not able to open via sharing to OneDrive or Dropbox, I will see if it can be recovered.