The techniques disclosed herein provide enhanced security features for controlling access to shared content and private content of a document. A system can enable multiple users to access a common content file, such as a Word document. Each user can add additional private content unique to each individual user. Private content associated with a particular user is restricted from being shared with any other user. Thus, when a first user opens a file authored and/or owned by other users stored in a cloud storage service, the system allows that first user to see the common content that is shared by the other users plus private content that is unique to the first user, but not allow the first user to view other private content provided by the other users.