The marketplace is flooded with non-Adobe PDF writers that promise to convert practically every file format into PDF.
Like Acrobat, you can install these third-party PDF generators [1, 2, 3] as virtual printers and create PDF files from any application that has the Print button. Some services go a step further - you send them a file as an email attachment and they'll mail it back to you as a PDF.
That's not all. WordPerfect and OpenOffice have in-built PDF printers. Microsoft released a free PDF add-in for all popular Office 2007 programs except Outlook. Then there are online suites like Google Docs and Zoho Office that allow you to save documents as PDF inside the browser without requiring any add-in.