This was announced by Microsoft on the Office blog in which they write, “We’re pleased to announce the ability to integrate Cortana in Windows 10 with Office 365 for businesses, available in the latest Windows Insiders preview build. Cortana in Windows 10 will be now able to connect to Office 365 to help you accomplish more at work.”
Basically with Cortana, users will be able to use it to fetch documents, send emails, and even show you upcoming meetings that you might have scheduled. Cortana has also been designed to be proactive and will be able to pull additional information, like information on the people you’re about to meet without you having to do anything on your own.
That being said, Microsoft also understands that sometimes there needs to be limitations to what employees are allowed to do, which is why they will allow office IT administrators to disable Cortana for Office 365 should they deem that the feature is not safe or unnecessary for their work.