Adobe Sign - Done everything but cannot get signed copy back

Just trying to implement signing of PDF documents via e-signature under a controlled environment.

I think we did everything:

• We created a fillable and with signature required PDF form using Adobe Acrobat
• Got Trial version of Above Sign
• Have a Adobe account
• Used Adobe Sign to send document for filled and signed PDF to another_person via email
• Document shows on Manage tab as sent for signature in Adobe Sign
• another_person received email with link and downloaded PDF document
• another_person opened PDF document using Acrobat Reader DC
• another_person filled and signed PDF document
• another_person saved the PDF document

• Now comes the problem: How does another_person get that filled and signed document back 2to the original user's Adobe Sign.

I am missing something here.

Thanks for any help