being in a similiar predicament at present with a client who is seeking my expert knowledge (does he know what he is letting himself in for...) about linking to site faqs via a PDF doc or a mini site i put these points to him and told him to discuss with his team and get back to me.
See points below and make your conclusion based on similarities to what you seek.
if a link to a PDF doc
1) on clicking the link you will not be taken to the point of interest but to the beginning of the document
2) the user may not be configured to view PDF docs (configuration or installation will be required)
3) who will update the PDF document to coincide with changes to html faqs
4) this will open a new window or overwrite main page site and not overwrite the Online Banking page
if using a micro site
1) here you can be taken directly to the point of interest when clicking on a link e.g. standing orders page help will take you to all SO references
2) update of the mini-site pages will need to be performed either by someone with html knowledge or via a CMS
3) this will open a new window or overwrite main page site and not overwrite the Online Banking page
hope this helps - if only a little 