Media files are already available to share between individuals and between groups from a long time. Now in the latest update of whatsapp you have the option to send pdf files as attachment under document tab.
To receive or send both the users should have on the latest whatsapp version otherwise one cannot send the pdf files as attachments. If you want to send pdf files inside a group, all members should be on the latest whatsapp version.
When you send a pdf file, recipients also see the preview in their message box along with no. of pages details.
To enjoy this feature update your whatsapp now.