Custom Inbound Attachment Callback Class
When you send an approval email using the Submit with Attachment feature, the attached document is sent to all approvers, who can only approve or reject the request. Approvers cannot modify the attachment. Even if the approver modifies the attachment and sends it to the next approver, the original attachment, not the modified one, is forwarded to the next approver. All approvers may also not agree on the same document by the end of the approval cycle unless approvals are submitted multiple times.
You can send modified attachments using the Inbound Attachment Callback. Inbound Attachment Callback allows you to write a callback class to handle attachments on an inbound approval email response. You can write custom logic to act based on the presence, absence, or type of attachment. This callback is called during approval reply handler processing.