Perfect!!
I had try it with regionManager.Regions["BackstageRegion"].Add(...) and then it will not find the region.
Its run perfect.
Second Question:
You use in your sample the "Office2016White"-theme. I can only use "Metro", because on the other themes it will not showing the File-button.
In your sample it will show. What does I need to use the other themes?
Have many thanks for your help.
Many regards Ronny