When adding a file using the File Picker, the default license type is "All rights reserved." According to some resources (such as the FAQs for the File Picker), this license type restricts the uploaded file such that it is not "available to others." This implies that things happen, programmatically, within Moodle to restrict access to files based on the license type, but there is no information available anywhere on just what restrictions are triggered and enforced by Moodle based on the different license types.