Probably not. Just because a regulation requires you to file something doesn't affect the copyright ownership of it. However, there may be an implied license to copy and archive the documents as public records.
In terms of intellectual property "public domain" refers to items that have no restrictions of use due to expiration of legal controls (patents, trademarks, copyright)
Pubic domain occurs naturally when a copyright expires. In theory, a copyright owner can intentionally disclaim any power to enforce a copyright, making it as if it were "public domain".
Read it, in private. Quote limited excerpts in reviews or educational materials. Re-sell or loan it (or, notably, burn it). Virtually all other uses would require permission from the copyright holder.