After you click 'View Phone Number' on any candidate's profile, you may click the Whatsapp icon and proceed to WhatsApp the candidate.
If you attempt apnaDatabase on your phone, you will not be able to do so. This product is available only on the website.
If you use apnaDatabase on your computer, you should sign into Web WhatsApp first or have the WhatsApp desktop application pre-installed.
To learn how to sign in to Web WhatsApp or install the WhatsApp desktop application, check the official WhatsApp FAQ: Here