Following in the footsteps of the Windows Phone app for Desktop, the Windows Phone app for Windows 8 has been updated. The new version adds the ability to transfer documents (e.g. Word, Excel, PowerPoint, PDF) to your phone. In addition it is also possible to open documents that are stored on your phone. The release notes also say that it is now easier to add "different types of files to your phone".
The Windows Phone app for Windows 8 app, which is used to copy content to and from a Windows Phone 8 devices, is best suited to those with a laptop or tablet running Windows RT, but can also be used by those Windows 8 users who want a Modern app style Windows Phone companion app. Other Windows 8 users mat prefer to opt for the desktop app, or a third party alternative.
Windows Store release notes:
The Windows Phone app now lets you browse documents, add them to your Windows Phone, and open files that are stored on your phone with other programs. We’ve also made it easier to add different types of files to your phone.