I have created a Process to run command in CMD.
var process = Process.Start(\"CMD.exe\", \"/c apktool d app.apk\");
process.WaitForExit();
How
You can use the WindowsStyle-Property to indicate whether the process is started in a window that is maximized, minimized, normal (neither maximized nor minimized), or not visible
process.StartInfo.WindowStyle = ProcessWindowStyle.Hidden
Source: Property:MSDN Enumartion: MSDN
And change your code to this, becaeuse you started the process when initializing the object, so the properties (who got set after starting the process) won't be recognized.
Process proc = new Process();
proc.StartInfo.FileName = "CMD.exe";
proc.StartInfo.Arguments = "/c apktool d app.apk";
proc.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
proc.Start();
proc.WaitForExit();