Putting a winform in front of another app window progmtcally

Question

Hello to everyone.

I'm looking for a solution to the following problem and i hope someone have any good tips for me:

I have inherited a legacy application, written in C with WinAPI, that draws a 2d animation inside a window on the screen. Now I have to develop (in C#) another application that simply draws some winforms with several buttons that have to be ALWAYS in front of the legacy window, i.e. if a user click on the window of the legacy application, my winforms have to remain foreground. I would avoid to modify the legacy application, and I would act only on the new application written in C#. The "topmost" option is only the very last chance.

Thanks in advance for each contribution!