var proc = new Process();
proc.StartInfo.Arguments = string.Format("{0} {1}", inputFilePath, outputFilePath);
proc.StartInfo.FileName = @Settings.GetImageMagickConvertPath();
proc.StartInfo.CreateNoWindow = false;
proc.StartInfo.UseShellExecute = false;
proc.Start();

proc.StartInfo.UserName = "user";

System.Security.SecureString secret = new System.Security.SecureString();

foreach (char c in "pass")
    secret.AppendChar(c);

proc.StartInfo.Password = secret;