While the best answer is "Don't do this," there are ways to make it more difficult for them. And since the point of this site is actually answer the question even if it's bad, here is the best way:
First you'll need to have the page open in a new window where you turn off the address bar and toolbar and everything else. That will make it so the user can't easily get to the File menu at all. To do this you'll need a "splash" page that the user loads to and then when they click a link, it opens the popup that serves the main content of your page. Details on how to create popups without things like the toolbar are here:
http://blazonry.com/javascript/windows.php
Then you'll want to add some javascript to each page that prevents the user from right clicking. Here is one method:
http://javascript.about.com/library/blnoright.htm
Finally, if it's your Javascript code that you don't want to be seen, then obfuscating your code is a pretty effective way to do that. They can still see the code if they have much know-how, but the obfuscated code would be a gigantic pain to actually interpret. There are lots of obfuscators out there; here is a free web-based one:
http://www.javascriptobfuscator.com/
This is far from foolproof. It will stop all "casual" users, but any power user will probably be able to easily figure out a way around it. Still if the idea is to at least prevent a good majority of it then this should suffice.
Update for updated question:
To address your new expanded question, I would say the best way to accomplish what you're saying is to use a format that supports DRM. Adobe Acrobat would probably be the best choice because almost everyone has the reader installed. You can prevent PDF files from being saved to the computer so that they can only be loaded from the webpage by a logged in user. The user could still do a screen capture of the document itself which I don't believe is preventable (unless Adobe Reader has some security in place for this, which they might) but it should be sufficient security for most uses.