PDF is Portable Document Format, a high-quality, printable document format that can be opened by anyone who has the free Adobe Reader application. PDF works by capturing printer data and storing it in a file, which is great for retaining the document formatting that you worked so hard to achieve. It also minimizes (but does not completely eliminate) the possibility that someone will modify your document.
Years ago, you had to buy Adobe Acrobat Professional to make PDFs. But then Adobe allowed the patent for PDF to expire, which opened the door to anyone else to create free PDF writer applications.
We have installed CutePDF on all Windows computers. To use it, select File --> Print in the application you are using and then select CutePDF Writer from your printer list. The option is not available in the Save As window!
Mac users should select File --> Print and then PDF --> Save as PDF.