There is only one file type that uses the .ONEPKG extension:
Microsoft OneNote Package File
Package file created by OneNote, a program that allows users to create and manage digital notes information; contains multiple OneNote files packaged into a single archive; used to publish notes to other users and to backup OneNote files.
ONEPKG files may be imported, or "unpacked", to a local folder by double-clicking the file and choosing the destination folder in OneNote.
|Microsoft OneNote 365||Free|
Updated: July 18, 2018