New version of Keynote and Pages won't open old versions

When using a newer version of iWork software such as on Yosemite to open older documents and presentations, Pages reports "This document can’t be opened because it’s too old. To open it, save it with Pages ’09 first." and Keynote reports "This presentation can’t be opened because it’s too old. To open it, save it with Keynote ’09 first." How can I open these files without finding and installing an old version of iWork?