Hello,
Try transferring the encrypted zipped .pdf to OneDrive. Afterwards install
http://www.windowsphone.com/s?appid=...4-cc62a0976d1e and select unpack - onedrive- unpack location and Ta Da. Pdf unpacked. Use MS app FILES to acces the folder and open with your favourite pdf app. Tested for ZipCrypto encryption method. Works very well.
On the other hand you can use the below method:
To download zip files to sd card/phone storage use Maestro (Preview) as e-mail manager. It's a very nice looking app and gives you the possibility to download zip files before opening.
http://www.windowsphone.com/s?appid=...9-1517c1d6aec0
It's in the preview status but works well.
Then use the steps fo unpack that I mentioned in the beginning.
Regards,
Me AV