Reader opens in two different ways: as a stand-alone application, and in a web browser. The associated work areas differ in small but important ways.
The Reader work area includes a document pane that displays PDFs and a navigation pane on the left side that helps you browse through the current PDF. Toolbars near the top of the window provide other controls that you can use to work with PDFs.
Select a PDF anywhere on the Internet and open it.
Choose File > Open (or Open File). If necessary, choose PDF or All Files in the pop-up menu for the type of file. Then navigate to and select any PDF on your computer or local network, and click Open.