Go to admin->Configuration Manager, then:
Authentication Settings->Disable DokuWiki actions
Check off the box for View Source
This will hide Dokuwiki's the View Source Button. But visitors will still be able to go to the Browser's view Source menu item and see the source.
What I am asking is how you are setting this:
<div style="visibility:hidden;"> ... wikitext here ... </div>
This is an HTML tag, and without a plugin can't be created from within Dokuwiki.