Why use numbers and words in docs, i.e. four (4)?

Question

Why in many documents, especially legal documents, do people use the word for the number followed by the same number in parentheses? For example, "After a period of twelve (12) months...."

Answer 1

To prevent someone adding an additional number within a space in the parentheses, words are included. This is especially so in cheques and important documents when big amounts of  money are involved.