How you open an existing publication depends on what you are doing in Publisher at the time. You can open a publication in many ways, most of which will be familiar to you from other 2007 Microsoft Office system programs:
In the Getting Started window, you can click a publication you have recently worked on in the Recent Publications pane on the right side of the window.
If the publication you want to work with is not listed in the Recent Publications pane, you can click From File at the top of the pane to display the Open Publication dialog box.
If you are working on one publication and want to open another, you can click the Open button on the Standard toolbar or click Open on the File menu to display the Open Publication ...