PDFCreator is a free tool to create PDF files from nearly any Windows application.
Key Features:

• 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
• AutoSave files to folders and filenames based on Tags like Username, Computername, Date, Time etc.
• Merge multiple files into one PDF
• Easy Install: Just say what you want and everything is installed
• Terminal Server: PDFCreator also runs on Terminal Servers without problems

And the best: PDFCreator is free, even for commercial use! It is Open Source and released under the Terms of the GNU General Public License.