>>Is it even possible?
No, the TextBlock doesn't translate HTML tags like <b>bold..</b> to bold text if that's what you are trying to do.
But you could use the WebView control and its NavigateToString method to load a local HTML string into it and display on your XAML page:
http://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.controls.webview.
Hope that helps.
Please remember to mark helpful posts as answer and/or helpful.