Many people think of Adobe's Portable Document Format (PDF) as a proprietary format for delivering unchangeable content that readers can print out or view on-screen conveniently. That may be how most people work with it, but you can do many more things with PDF, with or without Adobe's tools.

PDF has come a long way since it first appeared in the early '90s. When Adobe began offering its Acrobat Reader for free, PDF spread across the Web as a paginated alternative to HTML. PDF has replaced or supplemented Adobe's PostScript language files as a format for exchanging print-ready layouts, and evolving forms capabilities have made PDF a more interactive format over time.

Although most people still think of Acrobat when they think of PDF, the format has become a standard for other applications as well. Adobe publishes the PDF specification, so developers can create their own tools for creating and consuming PDF. Ghostscript software, for example, is an open source toolkit for working with PostScript and PDF. OpenOffice.org enables users to create PDF files from its applications, and Apple has integrated PDF tightly with Mac OS X, including its own PDF reader and tools for printing to PDF from any application.

Many people treat PDF documents as finished products, simply reading them or printing them out, but you can create and modify PDFs in many ways to meet your needs. Adobe's Acrobat family of products, beyond the Acrobat Reader, includes a variety of tools for creating and changing PDFs, but there are lots of other helpful tools and products for working with PDF, many of which are covered in this book.