I am planning to get a PC that can play latest games smoothly (not extreme gaming as it will go out of my budget), do some programming, internet surfing/downloading, document editing.
Dude.. that doesnt answer the query to understand your power requirements and therefore we cant tell you if 520W is enough for ur usage..
But I assume that you do not have the budget above 50K for your whole pc that will settle you down with a 7850/660/650TI at max on graphics front. In such case, Seasonic 520W will do the job for u.