Adobe InDesign CS6 is a professional publishing tool that can handle anything from simple posters and PDF files, to brochures, magazines and books.
This version is all about more easily reworking layouts to suit a range of page sizes, orientations and devices. You're able to easily create multiple versions of a layout within a single InDesign file; "liquid page rules" can automatically reorganise your content to suit a new layout size or orientation; and a split window option means you can compare two layouts side-by-side to make sure they're delivering the consistency you need.
Document creation has been extended and improved in many ways. The Content Collector and Content Placer make it much easier to reuse text and objects from an existing layout (or web page), into a new one; frames can now expand or shrink automatically to fit your text; you're able to create PDF fields directly from within InDesign; and your layouts can now include interactive HTML (and that interactivity remains when you export to HTML, EPUB3 or .folio for Adobe Digital Publishing Suite).
If all this is getting a little too complex, then you'll appreciate the new linked content option: once linked, any changes made to the parent (I don't like that yellow background now, let's have blue instead) are automatically applied to the child objects.
And there are all kinds of smaller, though still welcome tweaks. Recently-used fonts now appear at the top of the fonts list, for faster access; Hunspell dictionary tools place more than 100 open source dictionaries at your fingertips; and when you've finished then you may export your document to PNG for easy use online (or anywhere else that might be convenient, really).
Note that the download for Adobe InDesign 6 is a "download manager" which installs to your computer, requires you to login with your Adobe user ID and password, and then choose the components you want to download and install. Patience may be required.