To password-protect PDFs (the recipient must provide the password in order to open it), go to the company's settings to the Miscellaneous tab:

Check the box Protect PDFs with a password.

From this moment on, you can assign passwords to employees in tab 10 of the employee management:

If you click on Generate, it will generate a random password consisting of numbers, upper and lower case,

It is also possible to type something. It lets you (or the employee) choose the password.