Notes about the NDK file extension:
Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The NDK file type is primarily associated with 'Notes' by IBM. This was a Lotus product. Lotus was bought out by IBM. Lotus Notes and Domino are a fundamental component of IBM Workplace. This file replaces .DSK files which were used by Notes for a long time. Windows XP and OS/2 adopted .DSK files for system backups and Notes had to change to avoid confusion.