Want to generate a pdf with Ajax response not getting in proper format

I am getting a response like that i have attached image please check it and give me solution to convert in json

Code.

Ext.Ajax.request({method : 'POST',url:''withCredentials : true,defaultXhrHeaders:{'Content-Type': 'application/x-www-form-urlencoded'},disableCaching : true,success: function(response){}});