When you create a notebook in OneNote 2016 it’s automatically saved in the new 2010-2016 file format. You’ll need this format if you want all the features in OneNote 2016 to work properly.
The new file format is named “OneNote 2010-2016 notebook format” to let you know it’s compatible with the OneNote 2010 and 2013 formats. OneNote 2016 can read notebooks created with either OneNote 2016 or 2013 and it can also open, view, and edit any notebook files saved in the older OneNote 2010 and 2007 file formats.
Tip: If you’re upgrading from OneNote 2007 to OneNote 2016, your existing notebooks in the 2007 format won’t be automatically converted. This is to make sure you can use OneNote 2016 for all the notes you’re currently working in, including collaborative projects with people whose shared notebooks are saved in the older format. If you're still sharing notes with people using OneNote 2007, postpone upgrading the notebook file format until all others have upgraded to OneNote 2010 or later.
To check which file format a notebook is saved in:
In OneNote 2016 or 2013, open a notebook, and look at the title bar of the OneNote window. If [Compatibility Mode] is shown next to the notebook name, the notebook is saved in the older 2007 format.
In OneNote 2010, choose File > Info. Next to the name of the notebook you want to check, choose the Settings button, and then click Properties. In the Notebook Properties dialog box, look at the Default Format to see what format the notebook is saved in.