Don't bother. Windows 8 mobile won't run generic Windows apps. Apps must be specifically developed for Windows 8. APM planner is not.
To run APM Planner on Windows 8 you need a full pc version. Won't work on tablet (non-pc tablet) or phone.
As long as it runs Windows 8 PC (or whatever they are calling it)
Isn't APM Planner written in Java? If so, it should be relatively easy to port to the HTML5 display format of Windows 8 Mobile / RT.
APM Planner is written in C#.NET
In that case I'll take a look at the code. Do you know which version of .net?