Special utilities like WhatCrypt Tools allow users to convert / recover various WhatsApp message backups (.crypt12 file extension) and save the chat history as .zip file that contains the chats in a HTML format that you can view using any web browser.
Once you get the HTML file, you can use it in MS Word or any other suitable word processing program and save it as standard document (.doc or .docx format).
Open CRYPT12 file Open DOC fileOnline service for WhatsApp databases