WhatsApp allows you to send documents to your contacts, just as you would send media, contacts or a location. Please keep in mind that WhatsApp only supports sending PDF files at this time.
Note: The maximum allowed file size is 100 MB. In order to send a document, the document must be saved locally on your phone.
Documents are saved in your phone automatically once they are received and downloaded via WhatsApp. If documents aren't set to be downloaded automatically, tap the Get Document button on each received document to download it.
Once a document is downloaded, you will be able to forward it: