Something as simple as opening a PDF file can infect your computer, and potentially allow malicious hackers to gain access to your corporate network.
Cybercriminals create boobytrapped PDF files, exploiting vulnerabilities in PDF reading software such as Adobe Reader, and either spam them out to unsuspecting victims or plant them on websites where they lie in wait for visitors.
Just the simple act of opening the PDF file can exploit a vulnerability to automatically download malicious code from the internet, and display a decoy PDF file to trick you into believing that nothing wrong has happened.
Check out the following video by our own Chet Wisniewski, showing how a PDF can help hackers pwn your PC:
Read more in my article on the Naked Security website.