One of the nice things about OS X is the ability to print to PDF files. This saves paper, is great for searching with Spotlight, and even sending files. However, if you have some sensitive data, you may want to encrypt the PDF file. Perhaps you have a tax return, business contacts, etc. It's even great for sending sensitive data via email.
Here is how to do it: Find something worthy of encrypting. Open the file, web page, or whatever type of document it is. Bring up the PRINT dialog box by going to 'File -> Print'. (standard on most apps). Now, instead of clicking 'Print', click on the PDF drop down, and choose 'Encrypt PDF'. Now, your document will be processed, and it will prompt you to enter a password for it. Enter in a good password, and then press tab, and enter it in again, so that they match. If the box says they don't match, hit the tab button again. I found it doesn't change unless you do that. If they are the same password, you will get the 'The Passwords Match and are Valid' message. Then click 'Continue'. Now, choose a location to 'Save' your file. If everything went as planned, you now have an encrypted PDF. When you try to open it, you will be prompted for your password.