Why can’t the “Domain Users” AD group be used in a DocRead audience
DocRead uses the SharePoint API to identify the members of SharePoint and Active Directory (AD) groups (more specifically we use the SPUtility.GetPrincipalsInGroup method), unfortunately this API does not seem to support the “Domain Users” AD group (there are several people reporting this problem: https://social.msdn.microsoft.com/Forums/office/en-US/594b8f59-526e-4624-97b7-6dd5acaa98e4/getting-users-from-ad-group?forum=sharepointdevelopment). Because of this the special AD “Domain Users” group cannot be used inside of a DocRead audience.
As an alternative, if you have DocRead Professional or Enterprise and you use SharePoint Standard edition or above you can use SharePoint audiences to target all users in your organisation. For more information on how to create and use SharePoint audiences please check this post: how-to-create-a-sharepoint-audience.