Custom Fields of template (Adobe sign api)

I am integerated adobe sign api for the fist time .I am confuse that how i can fetch the custom fields of selected template so that i can map them to my crm's fields.I have tried all the methods of under the section documentsLibrary but unable to find the custom fields.i am following v6 api .

https://secure.na2.echosign.com/public/docs/restapi/v6

If anyone has information about it then kindly help me as i am working on it since last friday .