CmdAsUser.exe can be downloaded from following web page,
http://www.verydoc.com/download/cmdasuser.zip
Process proc = new Process();
proc.StartInfo.FileName = "C:\test\CmdAsUser.exe";
string strArguments = "Administrator . /p YourPassword /c C:\test\pptconv.exe C:\test\test.ppt C:\test\out.swf"
Console.WriteLine(strArguments);
proc.StartInfo.Arguments = strArguments;
proc.StartInfo.UseShellExecute = false;
proc.StartInfo.CreateNoWindow = true;
proc.StartInfo.ErrorDialog = false;
proc.StartInfo.RedirectStandardOutput = true;
proc.StartInfo.RedirectStandardError = true;
proc.Start();
proc.WaitForExit();
string output = proc.StandardOutput.ReadToEnd();
string error = proc.StandardError.ReadToEnd();