How to use PresentationSource?

Question

C++ / C#

I am making an application and I need to get the scale of the interface so that the program correctly takes a screenshot of the entire screen. To do this, I found many ways, but they are all not working, as a result, there was 1 unverified:

double factor = System.Windows.PresentationSource.FromVisual(this).CompositionTarget.TransformToDevice.M11;

but it says to me that there is no PresntationSource;