Merge Fields are used to pre-populate a signing document with some signer’s information like company name, address, patient record ID, etc…
These can be information collected by a client about their customers and fed into eSign API to be part of a particular signer’s information, and this can be anything about the customer.
Merge Fields need to be defined in a template first by giving them a key and default value, and then pass the desired values as part of the signer object in either the CreateSession or UpdateSession calls. The next version of merge fields will also be supported by anchor tags.
Please look at the code examples for the above two method calls in their corresponding sections.