The last version of iWork '09 (Pages '09 v4.3, Numbers '09 v2.3, and Keynote '09 v5.3) will work on all versions of High Sierra, and only on the last v10.14.5 and 10.14.6 updates of Mojave.
If your iWork '09 was originally installed from a retail DVD, then you can update those individual applications as mentioned above by installing the Apple iWork 9.3 updater. If your individual iWork '09 applications were obtained prior to Fall 2013 from the Mac App Store, then do not use the linked updater as it is incompatible.
The updater will introduce versions and autosave, the latter provided you actually save the document once.