Can I use conditional content within an article to hide content via a fixed password code?
For example I don't want my users to have to login, but I want to protect content within an article and if they have the passcode they can then see the content.
Conditional Content does not have a feature that displays a password field and such.
If you create that yourself, then yes, you can let Conditional Content check whatever data there is available (through PHP and for instance querying the database).