Ok if a film has no copyright and/or has fallen in to public domain (like Night Of The Living Dead) does that mean that some one could make a word for word/ shot for shot remake or parody and not have to get permission?
Simplistically, the owner/holder of a Copyright is the only person/body with the right to copy the work in question, or substantial extracts of the work, or to give permission to another to do so.
If no copyright exists then everyone is free to copy unhindered.
"Night of the Living Dead" has lapsed into the public domain due to a technicality. The original distributors didn't put the correct copyright notices on the original prints & they expired. This loophole has now been closed and now you don't need a copyright notice any more.
To answer your question, yes they could do a remake without permission. Ironically, any new version of it can be copyrighted.