You can open a PDF from within the Reader application, from the desktop, or from within certain other applications.
Choose File > Open, or click the Open button in the toolbar. In the Open dialog box, select one or more filenames, and click Open. PDF documents usually have the extension .pdf.
(Windows) Choose File > [a previously opened PDF].
(Mac OS) Choose File > Open Recent File > [a previously opened PDF].
To open a PDF attached to an email message, open the message, either by double-clicking the PDF icon or right-clicking/Control-clicking and choosing Open.
To open a PDF linked to an open web page, click the PDF file link. The PDF usually opens in the web browser.
Double-click the PDF File icon in your file system.