When you attach a digital signature to a file, you are helping to ensure that recipients of the file are notified of modifications.
You can set an option for a signature to be attached after you save a file. A single digital signature can be attached per file.
If you plan to protect a set of drawings with a password and a signature, first add the passwords, and then sign the files in a batch. Adding a password to a signed drawing, or otherwise changing a signed drawing, invalidates the signature.