PDFCreator is a free tool to create PDF files from nearly any Windows application.
Create PDFs from any program that is able to print
Security: Encrypt PDFs and protect them from being opened, printed etc.
Send generated files via eMail
Create more than just PDFs: PNG, JPG, TIFF, BMP, PCX, PS, EPS
Merge multiple files into one PDF
Easy Install: Just say what you want and everything is installed
And best of all: PDFCreator is free, even for commercial use! It is completely Open Sourced.
The program and its source can be downloaded for free directly from here.