WhatsApp in the latest version of the application gives the user the provision of sending text files and document through the application itself. In order to get the feature update your WhatsApp to the latest version from Play Store. It is now available for all Android users. if your phone is not getting the latest version, you can directly download it from the whatsapp website. (See the link for help).
In the new version, clicking on attachment from the chat window will show additional options to attach document.