I recommended it.

No, that is the correct code. It's an absolute server path.
Type that into your browser and see if it gives you the password protect page.
As you can see, this is the password protect page:
http://vonweizer.110mb.com/password_protect.phpMake sure the page you want to protect has the .php extension, it must be a .php page to work.

Just to make sure, your not adding the code to your pdf document are you?
To protect the pdf completely you must have .htaccess , otherwise somebody can just type the address to the pdf in their browser directly.
Edit: Your trying to protect your index, but it has a .html extension and not a .php extension.
