Documents can easily unarchive any compressed .zip or .rar files for you. To unarchive a compressed file, simply tap it. To learn more about unarchiving process in Documents, follow this article.
To add a compressed file to Documents, you can either compress files or folders in the app or use one of the following ways:
To unarchive a compressed file, simply tap it, and unarchived files will appear in the same folder where the original archive is located. If you don't need this archive anymore, you can tap ... on it, then tap Delete. Provided that you had unarchived the file, all the unarchived files will stay untouched, while the archive itself will be deleted.