Update IWorks

Was this a new, 2018 Mac mini purchase, or an older machine? When you look at the Pages application icon, which icon is present — Pages '09 on the left, or Pages v5 thru v? on the right?

From menu : About This Mac, what information is shown on your panel?

On macOS Mojave, Pages '09 simply can no longer open or create new documents, and is effectively broken. You can only download the Pages, Numbers, and Keynote from the Mac App Store if you have High Sierra (10.13.6) or later already installed.

The Pages, Numbers, and Keynote in the Mac App Store have now been free for several years. The only trademarked iWork applications were on the iWork '08 and iWork '09 DVDs, or prior to October 2013, individual purchases of these applications from the Mac App Store. These iWork 'YY applications were retired in Sept 2013. Since October 2013, Apple has dropped the iWork naming of these three applications.

There are dedicated Pages/Numbers/Keynote for Mac communities. The support community has left the iWork trademark because users are still active with the older iWork, and newer applications.

Search for the three apps - Pages, Numbers, and Keynote - on the App Store. When you go to download them, it should tell you whether they are available as an upgrade/free download, or if you will have to pay. Usually if the app is already installed on the system it should show up in the App Store as an upgrade, but perhaps not if the old version is too far behind.

Alternatively, you may be able to launch one of the old Apps and find "Check for Updates" in the menu, but it will likely take to the same place in the app store.