Encryption in Microsoft word is just securing your Microsoft word document with a password that only you or any other person you give the password to can access the document.
Open the document you want to encrypt/secure with a password
Go to File on the Microsoft word Menu
The Save As option should pop up
Go to Tools
Different Options will pop up
Click General Options
A new interface will pop up again showing where you can input the password you want to use to encrypt/secure your document
Type your desired password in the field provided
Input the same password to open and to modify.
If you want to Read-only then click the Read-only box
Then Click Ok.
And Then Save on the Save As pop up
You have encrypted/secure your document. No one can access the document without your permission (without you giving out your password).
NOTE: Use password that you can remember, because if you forget the password, you cannot gain access to the document.
If you have enquiry/questions comment below and I will answer ASAP