PDF files do not display as attachments
I have installed Acrobat reader, and then deleted and reconfigured my 2 email accounts (pop3 and exchange).
PDF files are presented as "winmail.dat" files in my new - iPad air
iPad Air Wi-Fi
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 😉