Adobe InDesign CS6: Saving / Exporting for InDesign CS4,CS5 and CS5.5
This is more of a quick tip than an actual tutorial but today I will quickly show you how to export or save your InDesign CS6 documents for earlier versions of InDesign. This simple method will allow you to open your files in InDesign CS4, CS5 and CS5.5.
Go to Files > Save as
In the dialog box that comes up at the bottom in the Save as Type: drop down menu select InDesign CS or later (IDML). Name your file and hit save.
If you are using InDesign CS5.5 or before and want to be able to save back as far as CS4 use File > Export then follow the rest of the steps exactly the same.