Download original offer letter from onboarding journey

Summary:We have one requirement that in recruiting in offer stage we will send the preliminary offer letter to the candidate.After accepting the offer,once the candidate move to HR and converted to employee and onboarding journey triggered.Then from the onboarding journey task the candidate/employee can download the the original offer letter which is different than the preliminary offer letter which we extended in offer stage to the candidate.The original offer letter in the onboarding task should be electronically signed and save into the the employee's document of record.

Any idea how to achieve this scenario