Information
This policy setting controls whether Office users can add password encryption to documents. (Users would access this feature in Microsoft Office tab--click Info, click Protect Document, then click Encrypt with Password.) The recommended state for this setting is: Disabled. If Office users add passwords to documents, other users can be prevented from opening the documents. This capability can provide an extra level of protection to documents that are already protected by access control lists, or provide a means of securing documents that are not protected by file-level security. By default, users can add passwords to Excel workbooks, PowerPoint presentations, and Word documents from the Save or Save As dialog box by clicking Tools, clicking General Options, and entering appropriate passwords to open or modify the documents. If this configuration is changed, users will not be able to enter passwords in the General Options dialog box, which means they will not be able to password protect documents.
Solution
To implement the recommended configuration state, set the following Group Policy setting to Disabled. User Configuration\Administrative Templates\Microsoft Office 2016\Security Settings\Disable Password to Open UI Impact: The recommended settings enforce the default configuration, and therefore will not affect usability. Typically, this setting should not be enabled, because doing so will prevent users from adding passwords to Office files. However, if you wish to ensure that only other mechanisms are used to secure files, you might consider enabling this setting.