What is the difference between the Owner and User passwords in a PDF document?

The standard security provided in a PDF document consists of two different methods, each with its own type of password. 

1. The User password controls the ability to open the document. This password encrypts the file and prevents someone without the password from reading the content.
2. The Owner password controls operations within the document.  This password specifies which features and functions within the PDF document are available to the reader even after the document is opened. With the owner password you can allow someone to read a PDF document but prevent that person from printing it, copying text or graphics, changing the document, or adding or changing text notes and AcroForm form fields.