Click on button redirect to another page in Salesforce.

Hi Up,

If you are calling controller method from lightning component then you can not return Pagereference from that controller method because AuraEnabled methods do not support return type of System.PageReference.

Workaround-

You can open any link from your callback of javascript controller

action.setCallback(this,function(response){
if((response.getState()=="SUCCESS")&&(component.isValid())){
if(response.getReturnValue() != null){
window.location.href = 'your link';
} }
});