Contracts theoretically could be protected by copyright. However, we reuse so much of the functional language that it would be difficult to prove that a given contract is sufficiently transformative to merit protection. One exception is that heavily-annotated firm templates and file memos. I would be more cautious about sharing a detailed, annotated template from a previous employer.

Some large firms in fact do require associates to sign covenants. In particular English firms seem to do this a lot. I consider it to be unethical, as it is anti-competitive and runs contrary to the interests of clients, who should remain free to select the lawyer of their choice (even a disloyal employee of their previous law firm).