Any material created by a person, or organisation (including text, pictures, diagrams, music etc) and made available to the public, i.e published, is covered by copyright law. This includes both print and electronic material.
Copyright is normally owned by the publisher of the material, and copyright restrictions usually remain in force for 70 years after the death of the authors. There is also copyright in typographical arrangement (the publisher's layout) which lasts for 25 years.
Copyright law imposes restrictions on how you can use published material. You can only upload this material to Moodle if you have explicit permission from the publisher, or if a user licence or explicit copyright statement allows it.