If you want to update the information about the signer in records after the recipient signs and sends the agreement across, use the getCustomTabs APIs. getTabs for each Recipient: Enables you to retrieve the values set within input tags for a field in the contract when the request for eSignature is completed.

The snippet below enables you to fetch and update the information of a signer:

/*
* Sample class for demonstrating how to get the values from DocuSign custom tags 
* and update the custom fields on DocuSign Default Recipient object on an Apttus Agreement
*/
global class DocuSignEnvelopeGetRecipientTabs2Imp implements Apttus_DocuApi.IDocuSignEnvelopeGetRecipientTabs2{
global DocuSignEnvelopeGetRecipientTabs2Imp(){

} 
global void getRecipientTabs(List<Apttus_DocuApi.GetRecipientTabsWrapper> iListGetRecipientTabsWrapper){


Set<ID> setParentId = new Set<ID>();
for(Apttus_DocuApi.GetRecipientTabsWrapper objGetRecipientTabsWrapper : iListGetRecipientTabsWrapper){
try{
ID parentId = ID.valueOf(objGetRecipientTabsWrapper.parentId);
if(!setParentId.contains(parentId)){
setParentId.add(parentId);
}
}catch(Exception ex){
System.debug('ERROR : it is DEMO...!');
}
}

List <Apttus_DocuApi__DocuSignDefaultRecipient2__c> listRecipients = [SELECT Apttus_CMDSign__AgreementId__c,Apttus_DocuApi__ReadOnlyEmail__c,Apttus_DocuApi__SigningOrder__c,CustomTab1__c,CustomTab2__c,CustomTab3__c from Apttus_DocuApi__DocuSignDefaultRecipient2__c where Apttus_CMDSign__AgreementId__c in :setParentId];
Map <String,Apttus_DocuApi__DocuSignDefaultRecipient2__c> recipientMap = new Map <String,Apttus_DocuApi__DocuSignDefaultRecipient2__c>();

for(Apttus_DocuApi__DocuSignDefaultRecipient2__c r : listRecipients){ 
String strKey = r.Apttus_CMDSign__AgreementId__c + String.valueOf(r.Apttus_DocuApi__SigningOrder__c);
recipientMap.put(strKey,r); 
} 
List<Apttus_DocuApi__DocuSignDefaultRecipient2__c> toUpdate = new List<Apttus_DocuApi__DocuSignDefaultRecipient2__c>();
for(Apttus_DocuApi.GetRecipientTabsWrapper objGetRecipientTabsWrapper : iListGetRecipientTabsWrapper){ 

try{

ID parentId = ID.valueOf(objGetRecipientTabsWrapper.parentId);

System.debug(System.LoggingLevel.ERROR, 'Parent Id == > '+parentId);
Apttus_DocuApi__DocuSignDefaultRecipient2__c docuSignDefaultRecipient = null;
System.debug(System.LoggingLevel.ERROR, 'Step 001 == >');

Apttus_DocuApi.DocuSignUtil2.DocuSignRecipientStatus objRecipeintStatus = objGetRecipientTabsWrapper.recipientStatus;
System.debug(System.LoggingLevel.ERROR, 'Step 001.1 == >');

String strKey = parentId + objRecipeintStatus.routingOrder;

Apttus_DocuApi.DocuSignUtil2.RecipientTabs rTabs = objRecipeintStatus.tabs;

//check if the recipient tab has text tabs

System.debug('Map values == > '+JSON.serialize(recipientMap));

if(recipientMap.containsKey(strKey)){
System.debug('Getting Map values for Id == > '+strKey);
docuSignDefaultRecipient = recipientMap.get(strKey);
}
if(rTabs.textTabs.size() > 0){
//populate the first custom field with the data in the first text tab
Apttus_DocuApi.DocuSignUtil2.textTab tTab = rTabs.textTabs[0];
docuSignDefaultRecipient.CustomTab1__c = String.ValueOf(tTab.value);

//populate the second custom field with the data in the second text tab
Apttus_DocuApi.DocuSignUtil2.textTab tTab1 = rTabs.textTabs[1];
docuSignDefaultRecipient.CustomTab2__c = String.ValueOf(tTab1.value); 
}

//check if the recipient tab has email tabs
if(rTabs.emailTabs.size() > 0){
//populate the third custom field with the data in the first email tab
Apttus_DocuApi.DocuSignUtil2.emailTab eTab = rTabs.emailTabs[0];
docuSignDefaultRecipient.CustomTab3__c = String.ValueOf(eTab.value);

}

toUpdate.add(docuSignDefaultRecipient);
} catch(Exception ex){
System.debug('ERROR AT the :'+ex.getMessage());
}
} // for

if(toUpdate.size() > 0){
update toUpdate;
System.debug('ERROR: UPDATE DocuSignDefaultRecipient: '+toUpdate.size()); 
} else{
System.debug('ERROR: UPDATE DocuSignDefaultRecipient: '+toUpdate.size());
}
}
}