You can't download WhatsApp for PC because this application doesn't exist anymore, but there is an alternative. Download Bluestacks and install WhatsApp into that environment. Bluestacks allows you to emulate Android giving you the possibility to install all Android apps through the pLay Store or the APK if you have the package instead.
Download Bluestacks, install it and configure a Google account then you can install WhatsApp. You need to have your phone nearby to confirm the installation through a SMS code.