After recently aouncing the ability for co-editors to chat with one another directly within a OneDrive document while working in Office Online, Microsoft today is extending this capability to Office 365 Business and Education customers for documents stored in OneDrive for Business or SharePoint Online, via Skype for Business. This feature allows you to chat with friends and family via instant messaging or video calling right from within a document. In addition, previous instant messaging history stays coected to the oarticular document, so that the next time the document is opened users can pick right up where you left off.
Read more about how to use co-chatting here.