Originally Posted by macropod

In that case, embed whatever you want into a document variable; they're only editable by code and, in the document itself, can only be displayed via DOCVARIABLE fields - and then only if you know the document variable's name. A more flexible but less secure storage medium would be a custom document property; they're accessible via File|Info|Properties>Advanced Properties>Custom and, if you want, can be displayed via DOCPROPERTY fields.