.PDF file arrives as winmail.dat

Get a winmail.dat decoder.

Search for winmail.dat in the app store. Here is on such viewer.

https://itunes.apple.com/app/winmail.dat-file-viewer-pro/id733258678

Ask the sender not to do that anymore:

Method 2: How to make a Per Recipient Change for TNEF

http://support.microsoft.com/kb/290809

iPhone, iPad, or iPod touch does not display attachment in email

http://support.apple.com/kb/ts1506

Email received from a sender using Outlook includes a Winmail.dat attachment

http://support.microsoft.com/kb/278061

You can use this app. Winmail File Viewer

https://itunes.apple.com/us/app/winmail-file-viewer/id379500151

 Cheers, Tom 😉