Charles Laughton plays Kidd, a merchant captain who cons the King of England (Henry Daniell) into allowing him to take to the sea to recover a lost treasure and escort a ship back to London. An old fellow conspirator who he thought dead (John Carradine) and a mysterious young man (Randolph Scott) manage to get on board and cause problems for Kidd.
You can stream Captain Kidd (1945) free and legally on OldReel, via the Internet Archive.
Yes — it is in the public domain and can be watched and shared freely.