You're not going to be able to use UWP APIs and remain compatible with Windows 7 or (I'm 99% certain) even Windows 8. Yes, Microsoft has introduced various ways to consume UWP APIs and controls in WPF and even plain old Win32 apps, some more hack-ish than others, but the resulting applications will still require Windows 10 to run.
If you need to stay compatible with Windows 7, you need to use plain vanilla WPF. Sorry! On the bright side, I've yet to find anything groundbreaking in UWP that can't be replicated in WPF satisfactorily.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…