Qiwen Zhang has Pocket Briefcase Pro (iTunes Link) for the iPad in the iTunes App Store for FREE (regularly $4.99) for a limited time.

Pocket Briefcase is an all-in-one document reader and manager for iPhone, iPad and iPod Touch.

It can import files from Camera, Photo Albums, PC/Mac(via Wi-Fi or iTunes), Email attachments, GoogleDrive, Dropbox,SkyDrive,Box and so on. All files are saved to your deivce locally so you can enjoy reading them anywhere!