Solution to updating old Keynote files
Here's the solution offered by a member of TidBits-Talk. It worked for me:
I discovered that after installing Yosemite, my old Keynote 4.0.4 files were not operating properly, and that when I tried them on a friend's computer who had upgraded to Keynote 6.5, the new version could not even open the old files.
After going through three levels of Apple support, I confirmed that only solution is to use the old program to export the old files as .ppt documents, then reimport them into Keynote 6.5.
That's not the only solution or the best one. Did you never have Keynote 5 (aka Keynote '09)? I'm not sure why Apple support wouldn't mention it. If you open then Save a Keynote 4 (aka Keynote '08) presentation in Keynote 5, you'll get a dialog that says "The document was created using a previous version of Keynote. To maintain the ability to open the document with earlier versions, click Save As and choose an application version." In this case you would not use the Save As button so the saved file will be converted to a format compatible with Keynote 5 and newer (i.e. Keynote 6). Saving updates the file you opened, it doesn't create a new one, so if you want to keep a copy in the original Keynote 4 format, make one before opening and saving in Keynote 5.
Keynote 5 ('09) still works on OS X Yosemite and you can have both it and the current version of Keynote on the same machine. In fact, if you double-click a Keynote file Keynote 6 can't open, it will say so and ask if you want to open the file in "Keynote '09" to save it. If you never bought Keynote 5 through the Mac App Store, you can't get it from there now. However, you can still buy boxed copies of iWork '09, which includes Keynote 5, online
http://www.amazon.com/dp/B0014X2UAK. You can also find online a free 30-day trial for iWork '09. If you just want to methodically convert all your Keynote 4 files to the newer format then switch to the current Keynote 6, the trial should be sufficient. Apple no longer hosts the downloadable trial, since it's no longer a current product, so you have to feel comfortable downloading from the site you find. Here's one example:
http://mac.softpedia.com/get/Business/Apple-iWork-06.shtml#download