title: How to send a pdf file on a WhatsApp number using c#.net
body: <p>I have created a web application using angular (for user interface) and c#.net.
  I want to send invoice (pdf file) on customer's WhatsApp no from my application.
  How can I send pdf file on file? I did go through some links but I did not understand.
  Any help would be appreciated.
  Thank you.</p>