What you can do with public domain works, and the limits

You can

Republish, sell and translate the text or film where it is free.
Write sequels, prequels, parodies and mash-ups using the free version of a character.
Record, arrange and perform free compositions without paying royalties.
Print free artworks on posters, clothes and products (in the EU, faithful photos of public domain art are free too).
Build products described in expired patents, and quote their drawings.
Use generic words that were once brands (escalator, thermos) in their generic sense.

Watch out for

Trademarks: names and logos like Mickey Mouse, Tintin, Nancy Drew or Agatha Christie are still brands.
New layers: modern translations, introductions, annotations, cover art, restorations and remastered audio have their own copyright.
Later versions: sequels and later designs stay protected until their own dates.
People: real people's names and faces can be protected by publicity or personality rights (Einstein, Marilyn Monroe, film stars).
Special laws: Peter Pan in the UK, French war extensions, Crown rights over the King James Bible in the UK.
Platforms: YouTube, Amazon and others may still flag public domain uploads; keep your proof.

Five ways to make money from fresh public domain

Be first with a clean edition. On 1 January, readers search for the new books: a well-typeset ebook or paperback, with an original introduction, wins the listing.
Add a layer you own. New illustrations, a translation, a study guide, an audiobook: the free work is the base, your layer is protected.
Adapt across formats. Novels into games, songs into lullaby albums, films into reaction or history videos.
Serve the markets that just opened. Agatha Christie in China or the Gulf in 2027, Dale Carnegie in Europe since 2026: local-language editions are open fields.
Ride the generic switch. When a drug or technology patent ends, price trackers, buyer guides and supplier lists get searched.

General information, not legal advice. Copyright, patent and trademark status differs by country, edition and translation: check before you publish or sell. Full disclaimer