Only the original is public domain, what you do based on it isn’t.
To keep the example Disney, Alice in Wonderland, the book, is public domain. So is One Thousand and One Nights, the story Aladdin makes use of. The films Disney made adapting them are not.
You can create your own adaptation of the books, or even just reprint them as is, but you can’t resell or modify the Disney versions.
Only the original is public domain, what you do based on it isn’t.
To keep the example Disney, Alice in Wonderland, the book, is public domain. So is One Thousand and One Nights, the story Aladdin makes use of. The films Disney made adapting them are not.
You can create your own adaptation of the books, or even just reprint them as is, but you can’t resell or modify the Disney versions.