My favorite method is using Open Office and exporting the item as a PDF.
There are a few other converters that will allow you to convert documents to PDF's one is called 'primoPDF'. -- if you're looking for making PDF forums, you're pretty much SOL, unless you wanna buy (or obtain) Adobe Acrobat Professional.
A better suggestion would be making a locked word document form, it works, but they look pretty crappy.