User Configuration > Administrative Templates > Microsoft Word 2016 > Word Options > Security > Cryptography
User
HKCU\software\policies\microsoft\office\16.0\word\security\crypto
This policy setting allows you to specify if a new encryption key is used when the password is changed. If you enable or do not configure this policy setting, a new intermediate key is generated when the password is changed. This causes any extra key encryptors to be removed when the file is saved. If you disable this policy setting, a new intermediate key is not generated when the password is changed.