A few of my Windows-using friends who can't be bothered downloading and installing software, and who don't need PDFs often, use this procedure:

1. E-mail me the file. (I have a Mac.)

2. I "print" the file, using the "Save as PDF" button that is standard in every print dialogue box.

3. I e-mail the PDF back to them.

Takes me a few seconds, I'm happy to do it for them within reason. Major limitation is that I need to have an application that will open their file, but so far it's always been for one component of Office or another.