If I purchase an app on my iPad can I get it on a Microsoft PC
Generally, no.

However the decision is ultimately up to the app’s developer to sell a single license across multiple platforms. So you’d have to check on a case-by-case basis (just don’t hold your breath).

As far as the actual executables, iOS and Windows apps run on completely different architectures, so there’s no way to copy an iPad app onto Windows and expect it to work. You can’t even do that on a Mac.