You've pretty much got it nailed.

To use Docusign on your engagement letters, you have two options:

1) do it separate just through Docusign and pay for that

2) get it signed at the end of the engagement (not recommended, but you CAN do this), by attaching it to the *Docusign* (not a PDF attachment in Lacerte return).  When you get ready to request eSignatures in Lacerte, there's an option to attach another document and manually set the taxpayer signature(s) on the signature line of your EL.

I use SmartVault for a secure file portal.  They also have an e-signature option that I haven't explored, but I think it's pretty much Docusign.

I put it on my clients to either hand-sign or their own e-sig software to sign the EL.  And for the ones that don't do either, I do option 2 above to clean it up on the back end and get signatures (only for faithful returning clients that I know will pay).