Exchange project files between different versions of Premiere Pro?
Basically what @Amer said plus for a shortcut there's an app that can 'downgrade' your project online - http://joshcluderay.com/downgrade-premiere-project-converter/
the trade off is, it always sets the version to 1 so 'some' effects and attributes might be lost in the process. I found that for your everyday editing this doesn't affect anything unless you're using titles (type).