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 configure the number of bits to use when creating the cipher key. This number will be rounded down to a multiple of 8. If you enable this policy setting, the key bits specified will be used. If you disable or do not configure this policy setting, the default value will be used.