Populate date field based on actual signature date

We're using document extraction to populate a Signature Date field with the date of signing via naming a form field with something like this: [Signer1.Capture1.label1.Date]. We're not able to use any template as we need to pre-fill client-specific values to the [pdf] document everytime which becomes readonly when presented to the client during signing ceremony. Now, we have a new requirement to dynamically populate a separate date field by adding a fixed # of days to signature date, which is to reflect right after signing. Is there a similarly auto-extraction approach (or API means) to achieve this?