Microsoft Windows Information protection - “helps to protect against this potential data leakage without otherwise interfering with the employee experience. “
More of the time data leakage will be situations where hackers , ex or existing empoloyees or third parties try and extract company owned data for their benefit or resales value. Some examples of this could be a recruiter extracting all his customers to take to a new company, a employee extracting his worked on projects so he has a base to continue them on as a contractor.
Other cases could be totally by accident , where an employee copies a file to an Unencrypted USB stick and loses it , or emails it home to a personal email so they can work on it later.
Devices enrolled in windows InTune can have policies set to protect specific files and only allowed them to be opened in applications that support information protection , such as the Office suit or Adobe Products. You can then set granular permissions on what is allowed to be done with these files such as only print.
You can also make sure that documents are only opened on Enrolled devices to InTune which makes sure documents never leave the Company on purpose or by accident.
If you have enrolled a device in Intune you should already have this as a license for free. It comes with the E3 mobility Security E3 License more price variables can be found here