You have several options to send a document with either an existing signature or sign it and then send it to other Recipients. There is the "Sign a document" feature or you add yourself as a Recipient (Needs to Sign) in the new envelope and add the appropriate Signature Tags to the document.

Alternatively you could scan and upload a document with an existing wet signature and send that document for further signatures through DocuSign. If you provide more details I can provide more direction.