Digitial Signature field Lost after document is scanned

Hi

I have a simple document with below workflow

Note: the digital signature(s) are assigned and is associated with email address.

-------- document start

1st Signatory  :     {{FST_es_:signer1:digitalsignature}}

2nd Signatory : Manual Sign, then scan and upload.  Manualy sign here -->

3rd Signatory : {{THRD_es_:signer2:digitalsignature}}

-------- document end

--- Workflow ----

A (Digital) -->  B (Manual & Scan, Upload) --> C --> (Digital)

Note: 1st and 3rd uses local digitial signature based on certificate

1st Signatory  --> System uploads as new aggrement and assign person A for digital signature. Person A signs using digital signature (local one created in acrobat reader)

2nd Signatory --> Post 1st signatory the document is downloaded by person B from internal system and person B now signs the document manually (hand) and scans and upload to internal system. System uploads the document to Adobe Sign as new agreement

3rd Signatory --> Post 2nd Signatory, system uploads to adobe sign as new agreement and sets person c as signatory . person C digitally signs the document

--- Workflow ----

Approach

For above worklfow the system is interacting on 1:1 basis i.e. all the signatures are not sent from adobe sign service.. rather sent one-by-one, (its the requirement of system)

Issue

The Person A digital signature cannot be validated when it reaches to Person C (after manually sign and scan by person B)

Question:

1) Is this a valid approach?

2) if yes, then what step is missing?

3) can you recommend a better approach  to tackle this? (Note: we already tried the approach where all the signatures are done in AdobeSign service, this is not valid in our case)

4) any other flaw you can point out?