PDFTK Builder Portable opens in wrong monitor

I moved PDFTK to my secondary monitor to do some work, and now every time it launches it opens in that second monitor (on the left edge).

For most apps, dragging the window back to the primary monitor and closing it solves the problem: the app will re-open in the place it was last closed.

However, this trick does not seem to work for PDFTK Builder Portable. No matter where I move the window, it reopens in the exact same spot on the wrong monitor. (Since this monitor is usually displaying another computer, this is a problem).

Does anyone know how I can get it to open in the primary monitor again?

Thanks!