Integrating WhatsApp for sending message through ASP.NET application

I am looking for help to use Whatsapp APIs to send Whatsapp message to students through my ASP.NET application. I expect a small working ASP.NET sample application that sends WhatsApp messages to a given mobile number on the form. So the form will have three fields Mobile number,text message, browse for attachment and Send button. I need to be able to send text message and image/audio/video/pdf/doc files.