Have a related question to this , how to reference these merge fields in the template pdf? Can you share the syntax for above example in document.

Also is there a way to use the Merge fields created while creating template from Docusign App launcher. If yes how to use them in Apex toolkit?

“dfsle.Tab.MergeField myMergeField = new dfsle.Tab.MergeField (‘Opportunity.First_Name__c’, null, null,false, false );`

  //Create a text tab that will be mapped to the merge field        
  dfsle.Tab myTextTab = new dfsle.TextTab()

.withMergeField(myMergeField) //Associate this tab with the mergeField
.withReadOnly(true) //true = read only or locked
.withPosition(new dfsle.Tab.Position(1, 1, 200, 300, null, null))
.withDataLabel('Contact_FirstName');`

/////////////////////////// In Document //////////////////

This is the document for //Contact_FirstName//