Enable Reader extended features and password protect

This is kind of a multi part question so bear with me.

I am working on a PDF Welcome Kit for new hires at our company. This document will be sent out via USB and email to new hires. It has a basic interface for navigating to the documents. The documents range from informational to interactive forms that need to be filled out.

I am creating this using Acrobat 8 Professional. I have Acrobat 9 Pro but need to make sure this document is compatible with 8 users.

The task I have is to do this.

1. Password protect the PDF so that when they open it, they have to type in a supplied password.
2. After they digitally fill out the eForms and click save it needs to retain the password protection (since the various forms will have their social security number).

My first was to set this up was to create the 13 page navigation PDF. I then placed all of the documents for them to review and fill out as attachments. I created links in the navigation so that when they clicked a button it would open the form up in a new window with the thought that they only need to fill out about 10 of the 40 documents attached, and they can then save the document and email back to us. This is the part where it needs to stay password protected without them having to re-assign a new password.

The other option was to keep the 13 page navigation and just add the 40 pages to the end of the document and have the nav. buttons send them to that page in the doc. vs open an attachment. And then have a Back button to get back to the navigation.

My main problem is figuring out how to Password protect the entire file, while enabling Reader features (write & save) and to keep the password protection on the document once they save it.

I'm open to creating this a different way and if i need to do it in Acrobat 9 I can move to that.

Thank You
Chris Riley