The Discover feature uses machine learning techniques to identify documents that are popular among people close to you in your organization. They are then displayed as search result suggestions on the Search Page in Outlook mobile. This can include both documents you have seen before and documents that are unknown to you.
You can see different types of content, but you can only see content you already have access to. At the moment you can discover PDF, Word, Excel and PowerPoint documents stored in OneDrive for Business or SharePoint. Please note that you will only see documents that you have access to and can discover through other experiences like search.
