First, you will need an Emulator to run Android apps because APK cannot run directly since it doesn't support stand alone apps and games either in Windows or Mac.
There are many emulators. However, you would want to read reviews and choose the best emulator that meets your computer configuration. I personally tried Bluestack, and Bluestack 2 but it lags. It takes a lot of time to start even in 4GB RAM PC with 100SST drive which is really a glitchy one.
Go for NOX emulator since it offers amazing extra accessibility from taking a screen shots, recording game play videos, installing apk directly from your computer and PlayStore or App store of you preferred OS etc. Comparing to all other emulators, Nox is a very fast, slick Android emulator available for both windows PC and Mac computers. If you're planning to use Nox for gaming, and for installing apps like social networking apps from Facebook to WhatsApp, you'll be pleased to learn that you can use your favorite game pad and apps and you have the option of mapping keys or buttons to perform various Android gestures too which no other emulator offers such extras and accesibilities. The emulator is based on Android 4.4.2 and works or support in Mac and Win.
Here is the Download Link [https://downloadnox.com/] to download. Once you download this file and installed on your PC, download the WhatsApp apk file from the NOX Google Play Store or if you have already downloaded the apk file then transfer it to your PC and install it manually.
For manual instalation, rename the app file with an extention .apk and right click> Open with> NOX Player
Hope that helps to run what's app in your PC.
Hackers never learns but always wins!