Need to render your file so you can composite it in another application such as an editing application? Be sure to choose a codec (compressor decompressor) that supports embedded alpha channels. Many users will prefer the animation codec as it provides a good balance of quality to size .
Click on the Output Module in the Render Queue
Choose Animation codec by clicking on the Format Options button and selecting it from the next window.
While there specify Millions + colors. Click OK.
The Channels menu should now say RGB + ALPHA and depth set to Millions of Colors +. If not, adjust them so they are properly set.
Your animation is likely pre-multiplied against Black so change it to set the color to Straight (Unmatted).
Click OK and Render when ready.