A more thorough explanation:

The acquired-rights doctrine is a principle that states that once a right has been obtained, it cannot be taken away by later legislation. This means that if someone has a legal right, it cannot be reduced or eliminated by new laws or regulations.

For example, if a person has a copyright on a book, they have the right to control how it is used and distributed. If a new law is passed that limits their control over the book, the acquired-rights doctrine would protect their original copyright and prevent the new law from taking away their rights.

The Universal Copyright Convention is an international agreement that applies the acquired-rights doctrine to copyright protections. This means that if a copyright was already in place before the Convention took effect, it cannot be reduced or eliminated by the Convention's terms.

Another example of the acquired-rights doctrine in action is with property rights. If someone owns a piece of land, they have the right to use it as they see fit. If a new law is passed that restricts their use of the land, the acquired-rights doctrine would protect their original property rights and prevent the new law from taking away their rights.