To create permissions within Word 365 so that only certain users within your organization can see the content and/or edit it. Once you have created your Word document go to the ribbon and click the Review tab.

Next, you can select Protect, which gives you 4 options: Protect Document, Always open Read-Only, Restrict Permission. When you select Restrict permission, you can then select Restricted Access.

A dialog box will open up, and allow you to select which user can Read, Change, or have Full Control of your document. You then select users using the book icon. Select the user or users you would like to have what type of access to your document, and click Ok.