Google Docs documents can be published on public sites. How does Google know the password to use (to get the document) when all you specify in the HTML is a string like: src="https://docs.google.com/document/pub?id=..." and no explicit password is used?
The document is set as public, so anyone who has the link can view the file.
Google Docs doesn't need to know your password in order to transmit the document to the person requesting it.
If you'd like to protect the document so that only certain people have access, view the document, then click File -> Share.