I’m able to edit and layout documents using Mac OS X versions of InDesign CS4 and CS5.
When doing this kind of work, I need licensed copies of all the fonts used in the document.
You can use the Package command from the Files menu to collate all the fonts – and linked images – used in InDesign documents into a single folder, for passing on.
Due to technical reasons, InDesign CS5 cannot open CS5.5 and CS6 InDesign files.
However, you can export InDesign CS5.5 and CS6 files using Adobe’s IDML (InDesign Markup Language) format for importing into CS5.
To do this, use the Export command from the Files menu.