The latest version of whatsapp have "send documents" features, you can send the pdf files directly using whatsapp. If you have files such as doc, xls, ppt, and also PDF, then you can send it using whatsapp directly on phone or using whatsapp web features if you want to send the files using pc/laptop.
If you want to send pdf files using whatsapp web, then you must access web.whatsapp.com on the browser.
Then open whatsapp - menu/settings - whatsapp web, then scan the QR Code. Until it connected like below:
Choose the recipients names, then tap on attach button, then choose the documents button:
Then choose the pdf files that you want to send., or you can also drag n drop pdf files.
Then tap send, to send the files.
For the receiver, it can open using phone, and also on the browser.
Ok that's it. Enjoy.