Peter Jackson's Lord of the Rings and The Hobbit trilogies made several changes to their source material, some of which were taken way too far. Though adjustments to canon are often necessary for book-to-screen adaptations, the works of J.R.R. Tolkien are heavily protected by the fandom. In many ways, Jackson remained true to the beloved author with The Lord of the Rings (though less so with The Hobbit), and what changes were made benefitted the story. However, other alterations missed the mark entirely.

https://screenrant.com/lord-of-the-rings-movie-book-changes-bad/