Adding New MIME types in WordPress Network
So running a WordPress install for K-12 you’ll often get asked to add new MIME types. There used to be some great plugins, but I haven’t seen any that are compatible with latest version of WP.
If you are running a network it is easy enough to force a function across the site by dropping a script in the mu-plugins folder.
Basically, I grabbed the code from http://netweblogic.com/other/adding-removing-allowed-filetypes-wordpress-media-library/ . I added all of the default MIME types and then added the additional ones I needed at the bottom (Notebook by Smart).
Drop the file in the mu-plugins folder, add the MIME types to your whitelist in the Network>Settings, and test with an upload of the appropriate file type.
The nice thing is that you can add new MIME types with out hacking core or limiting it to an individual blog template.
Here is the file that I used in my install.