There are several ways to encode your content in Dolby Digital Plus.
Here is our favorite list to get started with:
Avid Pro Tools - Mostly used for high end movie producing videos
Adobe Premier/Audition - Common solution for the mass market, and widely available
Encoding.com - Cloud solution that allows you to encode your existing assets. Purely used for file conversion
Azure Media Services - Microsofts Solution for developers already using their platform, purely used for file conversion