Hackers are choosing PDF files as their source for hacking. If your using PDF Adobe reader, then it is better to update periodically.
You can use Not only Adobe reader also Foxit Reader this reader available for FREE to download.
When you observe any unknow and doubted PDF files just to not open then go into Preference > Go to Trust Manager click option of Allow Opening of Non-PDF file attachement.
For foxit reader download check this link www.foxitsoftware.com