OS X version 10.4 or higher – With any document, in any application, go to the FILE menu and select PRINT. The PRINT dialog box appears.

In the bottom left of the PRINT dialog box, click and hold on the PDF dropdown, and from the sub-menu, select SAVE AS PDF…
The SAVE AS dialog appears. Give your document a file name (You do not have to add .pdf at the end of the file name. This is done automatically for you.)
Select the location for your document to reside, and then click once on the SAVE button.
That’s it. You now have a pdf document saved in the location you specified!