How to View Keynote Presentation Files Without Keynote Installed on Mac Using Preview
If you don’t have Keynote installed on a Mac but you need to view a keynote presentation slides or a keynote file, don’t fret – you can view them all directly in Preview, the bundled image app in Mac OS X.
Nothing special is required for this, just download a keynote presentation (.key file extension) and double-click the .key Keynote File to launch the slides into Preview
You can also drag and drop the keynote file into Preview app of Mac OS, if you have Preview already open, in the Dock, or if you have the Applications directory open as well.
From there you can view each slide independently, and if you put Preview into Full Screen mode you can even view the presentation as a slide show.
You won’t be able to make changes to the presentation slides, but if all you need to do is review slides this is more than adequate and saves you a couple bucks instead of buying the Keynote app.
The Preview application is located in the /Applications directory of Mac OS and comes bundled on every Mac.
This has been tested and confirmed to work in MacOS Catalina, macos Mojave, High Sierra, MacOS Sierra, El Capitan, OS X Yosemite, Mavericks, OS X Lion and OS X Mountain Lion, it may work in past versions but I just accidentally stumbled across it when looking at the 7″ iPad templates.
If you’re having difficulties or want to try on an older version of Mac OS X, try forcing Preview to open the file by holding down the command+option keys while dragging the .key document onto the Preview apps icon the Dock.