Finally, you can send document files via WhatsApp. With the latest version (version 2.12.453) of WhatsApp app, a new Document icon appears when you click on the attachment icon. Click on the document icon to attach file.
However, from my brief check, it seems that only PDF file can be attached and there is no way to change folder location. The default is the “Download” folder (although it is not stated). Nevertheless, this is a good start. Competitor apps like Telegram can already send many file types since some time ago. WhatsApp is now playing catch-up in this area. I hope that once it is stable, they can expand the attachment to different file types and able to change folder location.
In the meanwhile, please update your WhatsApp to the latest version to enjoy this little enhancement. Before I forgot, I think as of this writing, only Android is supported.