WhatsApp has been updated to add support for sending files. Yes, WhatsApp did allow sending documents, but you couldn't send any other file type before.
Of course, you could always rename the file to end in doc or PDF and send it, but it wasn't ideal. But with the latest update you can send files of any format be it a ZIP, or RAR, or even Android app APKs. And we did test it by sending an APK and it works just fine. There is a small caveat though, you are limited to a file size of 100MB per transfer, so that is a bit annoying.
But the new feature, which was previously being tested in the beta channel, does make things a bit easier. Be aware that the update is being rolled out slowly, so if you don’t get the update yet, wait for a while or opt in to the beta channel.
The version we used is WhatsApp Messenger 2.17.260, but to be fair we are in the beta, so that may be why we got it already. You can update WhatsApp for Android from the Google Play Store or the iOS version from the App Store to get the new file transfer feature.