I know I have to use SetWindowLongPtr with GWLP_WNDPROC and create my own WndProc that handles the message I want (such as WM_GETMINMAXINFO and modify the MINMAXINFO structure). However, because I want to do this for a window created by another program (like notepad.exe), I can't do this from my C#/WinForms program, I have to create a native C/C++ DLL that I have to inject in the the process that created the window.

Can you provide a link or the sample code to do this (the native C++ DLL and the way to call it from C# and inject it into the external process)?

Thank you