Adobe Pagemaker 7.0 is the last version of the venerable desktop publishing application. Although it is still sold and supported by Adobe, its functions are now covered by InDesign CS4.
It's made for designing things for print, from flyers and posters to reports, and will export creations as PDF files too. Like much of Adobe's output it is a feature rich program, but is quite inaccessible for the beginner. It does feature templates to work from, and that is recommended as a way to learn what you can do with it.
Adobe Pagemaker 7.0 was originally released in 2002, and it is showing it's age. It was designed for small businesses and professionals, and while it's adequate as a desktop publisher, the next generation of programs are more suited to today's world.
If you were happy using desktop publishing programs, you'll be pleased that Pagemaker is still available. However, for most people desktop publishing has become obsolete, as word processing applications can now create pages for printing ideal for the amateur user, and professional design suites are much better suited for business.
This is a perfectly viable publishing app, but it's relatively hard to learn, and out of date.