Dolby Audio Decoder Media Foundation Transform (MFT) is restricted under terms of the Dolby Digital licensing program to use by Microsoft applications for versions of Windows prior to Windows 8. You have to contact Dolby Digital directly for licensing if you want to have this decoder support in your own application. You can also consider to check for some third party solutions.
Third party applications are open to use both Dolby Audio Decoder MFT and Dolby Digital Audio Encoder MFT on Windows 8. Our MSDN documentation had some confusion about uses of these two MFTs, but recently we have updated it to clarify the confusion.