How can I soundproof a sliding bedroom door?
Sound or Water "Proofing" is very difficult. Cheap &amp; simple peel &amp; stick Weather Stripping will greatly reduce air (the majority of sound transfer) &amp; water intrusion. But, to get anything close to "Proofing" you need to have precision full contact around the entire door perimeter.

Sorry but, Star Trek was only a TV show. I'd suggest that you check with companies like this who are the masters of what you're asking &amp; yes you can buy their stuff off the shelf.