On the Mac, the easiest way to create a PDF file is to print the file in questions and choose the "Save as PDF..." option under the "PDF" button on the print menu. This creates a PDF file instead of actually printing. When you create a PDF in this manner, there is an additional button labeled "Security Options...". If you choose this button, you can add requirements to the document that a password be used to open and/or print the resulting PDF document. If you are looking to secure your documents, this is a quick and easy way to do so.