Do I notarize every page of a document? 

As a notary public, you notarize signatures on documents.  Generally, signatures are on the last page of a document, and there is some notary certificate wording below the signature section. If there is no notary certificate verbiage when you are notarizing, then you can attach a loose notary certificate with the official notary wording from your state.
 
What if the signature is in the middle of a multipage document?
With longer documents such as affidavits of support, living trusts, and other long documents, you are likely to see a signature in one of the internal pages of the document, and maybe another signature at the end of it, but not necessarily on the very last page.  Where do you attach a loose certificate if a signature is in one of the middle pages of a document?  It is normal to add notary certificates at the end of the document.  It is prudent to indicate on the certificate the page number of the document that has the signature you are notarizing with that particular certificate form.  Other notaries might use one certificate form to notarize all signatures in the document.  Which way is correct?  That is hard to say, but it is cleaner, if you have a separate notarization for each signature on a document that requires multiple signatures from the same person.  There might be separate agreements inside the same long document, making them more like separate documents that have been connected.
 
You can not notarize every page of a document.  However, you can use an embosser seal to make an inkless raised impression in all of the pages of a document you notarized, to safeguard from pages being switched after the fact.  This is a very prudent practice and I recommend it.

You might also like:

Notarizing multi-page documents
http://blog.123notary.com/?p=1706

Can I sign on a different day?
http://blog.123notary.com/?p=2457

Can a notary help draft documents?
http://blog.123notary.com/?p=2047

Sending loose certificates is illegal
http://blog.123notary.com/?p=2470