This is a fairly long post.  The topics to be covered are mentioned below. Complete Source Code will be uploaded in few days 

1. The Requirements ( this post )
2. How Adobe Esign Works
3. The Adobe Esign Solution
4. The Nintex WF Actions
5. Installation Instructions.

Through out the post , I will refer to SharePoint OnPremise as  SoP. Custom Nintex WF Action as NAction

Problem Statement 

We have a SharePoint 2013  On Premise installation.  Till very recently we were using on Premise Cosign as our E-signature solutions.  CoSign  was bought by DocuSign and a decision was taken  by Management to move to a new Esign solution

That left us looking for a different signing solutions for all the on Premise documents. The new solutions not only should let users esign the documents within SoP but also must have corresponding Nintex actions so that we could use this signing facilitity in the context of various Nintex WFs we had already written.  That means, we needed custom NActions just like old CoSign On Premise had. Also, as we are moving to SPO ( SharePoint Online ), we needed to make sure the new Esign Provider should have some story over there also.

We looked into two solutions.  Adobe Esign and Valid Sign.  Valid Sign had a strong case, because it already had replacement for those Cosign  Nintex Custom Actions which we  were using in our WFs. Adobe Esign on the other hand had a strong story on the Cloud part of the deal but nothing for On Premise solutions. Plus Adobe's licencing story was better suited to our case.  So due to these reasons we went for Adobe Esign.

That brings to the reason for this post. Adobe Esign is a complete cloud product. All the documetns to be signed by users, have to be uploaded to the Adobe Cloud. Adobe then manages sending emails to esigners, their signature etc. In nutshell, it was no interaction with SharePoint OnPremise. ( in fact it has some, but certainly not wrt Nintex WF )

So we ended up writing our own custom Nintex WF Actions to interact with Adobe Api. I assume if you are reading this process then you are aware of how Adobe Esign works. If not then read post 2.