On OS X, the process of duplicating a filename appends copy to the base filename.
Open the zonothings copy.pages document. In the Title bar, click the filename, and a panel appears with the name selected. Backspace just the zanothings copy part of the name and give it a new name. The file is renamed.
Alternatively, in the Finder, you can single-click the zanothings copy.pages icon name. Wait a second, and single-click it again. Just the zanothings copy part of the name is selected. Just type the new name, and press return to set it.