The NVivo software is forward compatible.  Project files (.nvp, .nvpx) created in older versions of NVivo can be opened and worked within newer versions of NVivo.

They are updated to the newer format automatically when the file is opened and by default the filename is appended with a version number to distinguish it from your old file.  A copy of your older version is preserved in its original location at the point of conversion.
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The NVivo software is not backward compatible.  If you are sharing project files with users of older versions, you will all need to be using the same version of the software unless your project meets the limitations of the REFI-QDA standard of qualitative data.

Data types not supported include audio, video, datasets and pdfs.