As Knorke mentions and the expanded passage explains, the article you referenced specifically refers to information stored on Microsoft Owned information systems such as that stored on servers that provide outlook.com email, or the file servers that house OneDrive cloud storage.
A few other good references can be found in the following links:
General overview of Privacy
Blog post from Terry Myerson, Executive Vice President, Windows and Devices Group which specifically says they WILL NOT use any data collected from your Email or OneDrive contents for targeted advertising.
If you actually read through most of it you can summarize a lot of the concerns you're asking about with the following:
Cortana/Bing report more or less everything you search or ask for. Each unique account requires a voice database to help with voice recognition and voice commands, if these features are activated. Cortana is considered a Bing enabled service, so it all gets lumped together under Bing, this may be included in the information MS provides to partners.
Data that leaves your hard drive and gets stored on their servers, be it files in your OneDrive, a live or outlook email address, is no longer really yours. Microsoft is legally allowed to examine that information to protect itself, comply with law enforcement, or prevent illegal activities without your consent. It can also be used to enhance services provided to you:
When you use OneDrive, we collect data about your usage of the service, as well as the content you store in order to provide, improve and protect the services. Examples include, indexing the contents of your OneDrive documents so that you can search for them later and using location information to enable you to search for photos based on where the photo was taken.
Taken from the Privacy Statement Knorke referenced earlier.
It is important to remember however, that is true of ANY cloud based, or third party provided, service. Google has the same power with Google docs and Gmail, Apple can do the same with iCloud and their mail servers. Unless explicitly stated in an agreement with a company providing a service to you (Typically this would be a business arrangement with a company, not a personal user). Once the data is on their servers they have implicit access to the data for a multitude of reasons.
To specifically answer OPs question though--Microsoft cannot randomly examine files from your hard drive that are not explicitly associated with a service designed to provide information to them, such as the search histories from IE/Edge, Bing, Cortana, etc... Contacts and Maps and many others (Too many to comprehensively list) keep local files on the computer which share information with MS servers. Most of the information Windows will share can be limited, or completely turned off via the Windows 10 Privacy settings, but as they say this can have a negative impact on user experience, suggestions, location based search results, etc...
Hope that helps a bit