All apps that were assigned to the user under Administration→ Apps are automatically part of the work profile (see article Add Android apps in the management console).
You can recognise the apps by the briefcase in the app icon (left illus.). In the work profile, business files cannot be moved into private apps (example in right illus.). Under Open in, the user will only be offered apps that are part of the work profile. Thus, private and business data are kept apart from each other.