Make fields editable by signer

I think this is an easy one as I think I am misunderstanding something fundamental.  How can I make a field editable?

This is populating the value correctly, but I want the signer to have the ability to adjust it:

            // printed name field
            OneSpanAPIObjects.Field printedNameField = new OneSpanAPIObjects.Field();   
            printedNameField.extract = true;   
            printedNameField.name = formSigner.Form_Signer_Printed_Name_Field__c;  
            printedNameField.type = 'INPUT';   
            printedNameField.subtype = 'TEXTFIELD';
            printedNameField.value = signer.firstName + ' ' + signer.lastName;