DocuSign is the only tool that seems to have this feature in its paid plan. DocuSign allows signers that “wet” sign a document to fax it back to DocuSign. The returned fax gets added to your records as a related document. Additionally, you can send documents via fax for signature. This feature is a part of Business Pro and Advanced Plan offered by DocuSign. This feature is free for Advanced Plans which is available on request or on a call. This feature is also available in Business Pro plan but can be availed only for an additional cost.