View Keynote Presentation Files Without Keynote Installed Using Preview in OS X
If you don’t have Keynote installed and you need to view someones keynote presentation slides, don’t fret – you can view them all directly in Preview, the bundled image app in Mac OS X.
Nothing special is required, just download a keynote presentation (.key file extension) and double-click it to launch the slides into Preview. 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.
This has been tested and confirmed to work in 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 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.