The PDF system does allow you to protect the contents of a PDF document with a password, encrypting the material so that it can be kept from prying eyes. Problem is, if you are already looking at a PDF that isn't password protected, how do you add a password to it?

The secret on the Mac is to print the document, but specify that you want the output as a new PDF document rather than a piece of paper. Bear with me and you'll see what I mean...

To start out, I pulled up a statement from my own bank, a PDF document that is displayed within my Web browser. Turns out this technique will work for any Web page so even if your bank produces HTML documents, you'll be fine.

While on the page, I Ctrl-Clicked on the background:

From here, select "Print Page..." to produce a print dialog pane:

Here's the trick. Don't click on the blue "Print" button, but instead click on the "PDF" button on the lower left...

Choose "Save as PDF..." (didja know all Mac apps can do this from the Print dialog?)

Enter a logical filename, then click on "Security Options..."

Here we go! Check the "Require password to open document" button then type in an easily remembered password - twice - and click on "OK", then "Save" on the other dialog box.

Now you'll have an icon on your desktop like this:

That's a secure PDF document. Double click it to open and you'll be stymied without the password:

More interestingly, try to preview the contents and that'll block you too:

It's a neat - and very helpful - feature of Mac OS X. Hope that helps you organize your paperless billing!