The files can be protected with a password.
To insert the password, select the File and accounting properties command in the "File" menu; insert the password in the "Password" tab, entering it another time in the "Confirm new password" zone. In this tab, the user can insert a new password by entering it twice to confirm it.
If, on the contrary, the user wishes to change an existing password, the old one has to be entered first before entering the new password.