From TAG:

By now, everyone’s antennae should stand at attention whenever an email lands in your inbox that has a file attachment. The latest attempt to install malware onto computers via email phishing campaigns is courtesy of the Russian hacking crew “Coldriver”. The email possesses an encrypted .PDF file that the recipient is urged to open – the hackers respond to the plea for help to receive the decryption password they reply with a malicious hyperlink that downloads/installs malware onto the recipient’s machine.

See website for complete article licensing information.