PDF may not be the only way, but it's free, platform neutral and by default difficult for the end user to edit.

I use Open Office for all wordprocessing, spreadsheets etc. one advantage of which is that it will export directly to PDF, but for any other application that prints you can use something like PDF995 which installs as an extra printer but "prints" to a PDF file. The demo is free and displays a nag screen each time you use it, but otherwise works well. You may not be able to suppress printing of the result but I don't think that's going to be a big problem.

Anahata