I am new to Bitcoin. How to integrate Bitcoin payment into my one of website which is designed using ASP.Net.
Also how to test it using Sandbox mode as provided by other gateways like PayPal?
If you don't want to integrate with a 3rd party bitcoin payment provider you can implement your own payment module for Bitcoin (but also for Litecoin and every Bitcoin-derived altcoin) very easily with BitcoinLib that is written in C#.
Some of BitcoinLib's features:
They will provide
Easy API - as opposite of bitcoind API which is intended for low level bitcoin tasks. If you are familiar with PayPal moving to other payment providers should be easy.
Fiat to bitcoin currency and vice versa
Address generation and matching orders to their bitcoin payments
Working with bitcoind directly from a web developer perspective is a little cumbersome, so I don't recommend it if you lack bitcoin experience.
You can use open source bitcoin/altcoin package from gourl.io:
It works fine in my project.