In North America, we are used to seeing novels published first and then adapted for the screen. In Japan, however, you will also find manga published first that are later adapted for film or novels. In that case you will often see the term ノベライズ (novelize)ノベライズ本 or 小説化 used in describing the literary version.
For example, Shogakukan has a series called 小学館ジュニアシネマ文庫 for students who want to read after having watched a movie.
ホームレス中学生 is an example of an autobiography that has been adapted into many forms: rewritten for children, released as a manga, and adapted for live action movie and shown as a television drama.
星守る犬 started out as a manga, was turned into a live action movie and later novelized.
告白 by 湊かなえ started out as a novel/short story, was turned into a live action film and later released as a manga as well.