Explanation:

- The original phrase "word by word" might be used in some contexts, but it’s less common when referring to exact replication of text.

- Option 1: "word to word" is not idiomatic for this context. It might imply words are connecting rather than exactly replicating.

- Option 2: "word for word" is the correct idiomatic expression. It means to copy something exactly as it is written, with no changes.

- Option 3: "word with word" is not a standard phrase in English for expressing exact copying. It suggests a pairing rather than copying.

- Option 4: "No improvement" is not suitable as there is a clearer alternative.