If you think you need expensive solution like Adobe’s Acrobat Pro to accomplish this on a Mac, well, you don’t. Because actually this capability was build in on your Mac OS. And it’s actually easy to use.
For example. Say you need to save a web page. What you need to do is to open the web page, then click on File then Print. A dialog window like this will open, then click the button like the image suggest:
You’ll get a dropdown choice like this, then pick Save as PDF…
You’ll be brought to another window like this, where you can add Subject, Keyword, Password etc for the .pdf file. Click Save and you’re done.