The short answer
A public domain work is free to adapt, but elements added later may not be: characters developed in later books, translations, illustrations, film versions, and trademarks on names and logos. Adapt from the public domain text itself, and clear anything you take from later versions.
Later works in a series
When a character appears across many books, each book enters the public domain on its own date. For years, the last Sherlock Holmes stories were still protected in the US while the early ones were free, and the elements that first appeared in the later stories could not safely be used. The final stories entered the US public domain on 1 January 2023, ending that split.
Visual versions and trademarks
A. A. Milne's Winnie-the-Pooh, published in 1926, entered the US public domain in 2022. What did not become free was the look of later versions: a red shirt, a particular drawing style, studio artwork from decades later. Adapting the 1926 book is one thing; copying a later studio design is another.
Trademarks are separate from copyright and do not expire on a timetable. A name or logo used in trade can stay protected for as long as it is used, so a title or a character name on merchandise needs its own check.
Translations, illustrations and editions
A translation is a new work with its own copyright, as are new illustrations, notes and forewords. If you build a script from a modern translation, you are adapting the translator's work too. Use the original or an out-of-copyright translation, or license the translation.
Restored US copyrights
Foreign works that fell into the US public domain for failing American formalities could have their US copyright restored in 1996 if they were still protected at home. A work that looks free in the US on its publication date may not be.
A short checklist
- Confirm the public domain date in every territory you will sell into.
- Work from the original text or a verified public domain edition.
- List every element you want that appeared later: characters, scenes, designs.
- Search trademarks for the title and character names in your markets.
- Have a clearance lawyer review the chain before you spend real money.
Questions
In the US, all of Arthur Conan Doyle's Sherlock Holmes stories have been public domain since 1 January 2023, and in the UK since Conan Doyle's works came out of copyright in 2001. Later adaptations and their original elements are still protected.
A name or design used in trade can be registered as a trademark, which is separate from copyright. That does not stop you adapting the public domain story, but it can limit how you use a name or logo commercially.
Not if the translation itself is still in copyright. The translator owns their translation, so use the original or an out-of-copyright translation.