"copy note 2 snote files into the note 3 storage folder called snote data (use MyFiles to go to All/Device storage/SnoteData). Now open your snote and you will find all the files. Just click on them and the files will get auto converted to note 3 format". From [Solved] Convert .snb to .spd ? | Samsung Galaxy Note 3 | XDA Forums
(Since the difference occurred as a result of going from 4.2 to 4.3, it should also work on the Note 4.)