I have created a Process to run command in CMD.
var process = Process.Start(\"CMD.exe\", \"/c apktool d app.apk\");
process.WaitForExit();
How
There are several issues with your program, as pointed out in the various comments and answers. I tried to address all of them here.
ProcessStartInfo psi = new ProcessStartInfo();
psi.FileName = "apktool";
//join the arguments with a space, this allows you to set "app.apk" to a variable
psi.Arguments = String.Join(" ", "d", "app.apk");
//leave it to the application, not the OS to launch the file
psi.UseShellExecute = false;
//choose to not create a window
psi.CreateNoWindow = true;
//set the window's style to 'hidden'
psi.WindowStyle = ProcessWindowStyle.Hidden;
var proc = new Process();
proc.StartInfo = psi;
proc.Start();
proc.WaitForExit();
The main issues:
cmd /c
when not necessary