I want to copy a file in my Google Drive using the web interface. Adding it to another folder seems to create a hard link rather than a file that can be changed independently of the original. There doesn't appear to be an action with a name like "copy," "duplicate," or "clone."
It appears Google have made this very difficult, I guess to stop the accidental creation of various versions of documents.
If the file is a Google format, you can open it and select File → Make a copy to duplicate it.
If it isn't, the only work around I've seen within the web interface is this cumbersome solution. (Only for files smaller than 25Mb.)
Right click file name in Google Drive > Share > Email as Attachment to yourself > open file in Email > Rename > save to Drive
Open Google Drive in the browser and select one or more files or folders.
You can use the Ctrl key on Windows, or cmd key on Mac, to select non-consecutive files and folders. Now press Shift+Z and you'll see an Add to Folder pop-up.
Select the folder where you wish to place the selected files and click OK.