MS Powerpoint Automation with Reflection

Question

I need to save powerpoints as HTML with c#. I also need to turn on animations with the 'ShowSlideAnimation' property. The first code block works fine, but when I duplicate the code with reflection, I am unable to get the 'WebOptions' property because it is null. I chose to do this without referencing the office assemblies because some of our clients may not have office installed.

Here is the code that works without reflection:

    var ppt = new Microsoft.Office.Interop.PowerPoint.ApplicationClass();
    var file = "C:\\Users\\username\\Desktop\\test.ppt";

    var presentation = ppt.Presentations.Open(file,
        Microsoft.Office.Core.MsoTriState.msoCTrue, 
        Microsoft.Office.Core.MsoTriState.msoFalse, 
        Microsoft.Office.Core.MsoTriState.msoFalse);

    // ShowSlideAnimation set successfully
    presentation.WebOptions.ShowSlideAnimation = Microsoft.Office.Core.MsoTriState.msoCTrue;

    presentation.SaveAs("C:\\Users\\username\\Desktop\\test.html", 
        PpSaveAsFileType.ppSaveAsHTML, 
        Microsoft.Office.Core.MsoTriState.msoFalse);

    presentation.Close();

Here is the code I am having problems with. I commented the lines that throw a NullReference exception. I cannot retrieve any PropertyInfo objects from the presentation object.

    var coreAssembly = Assembly.Load("office, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c");
    var pptAssembly = Assembly.Load("Microsoft.Office.Interop.PowerPoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c");

    var ppt = pptAssembly.CreateInstance("Microsoft.Office.Interop.PowerPoint.ApplicationClass");
    var presentations = ppt.GetType().GetProperty("Presentations").GetValue(ppt, null);

    var msoTriStateType = coreAssembly.CreateInstance("Microsoft.Office.Core.MsoTriState").GetType();
    var msoCTrue = msoTriStateType.GetField("msoCTrue").GetValue(msoTriStateType);
    var msoFalse = msoTriStateType.GetField("msoFalse").GetValue(msoTriStateType);

    string inputFile = "C:\\Users\\username\\Desktop\\test.ppt";
    string outputFile = "C:\\Users\\username\\Desktop\\test.htm";

    BindingFlags binding = BindingFlags.InvokeMethod | BindingFlags.Public;

    object[] openArgs = new object[] { inputFile, msoCTrue, msoFalse, msoFalse };
    object presentation = presentations.GetType().InvokeMember("Open", binding, null, presentations, openArgs);

    // presentation object contains zero properties
    //object webOptions = presentation.GetType().GetProperty("WebOptions").GetValue(presentation, null);
    //webOptions.GetType().GetProperty("ShowSlideAnimation").SetValue(webOptions, msoCTrue, null);

    var ppSaveAsFileType = pptAssembly.CreateInstance("Microsoft.Office.Interop.PowerPoint.PpSaveAsFileType").GetType();
    object ppSaveAsHTML = ppSaveAsFileType.GetField("ppSaveAsHTML").GetValue(ppSaveAsFileType);

    presentation.GetType().InvokeMember("SaveAs", binding, null, presentation, new object[] { outputFile, ppSaveAsHTML, msoFalse });
    presentation.GetType().InvokeMember("Close", binding, null, presentation, null);

    ppt.GetType().InvokeMember("Quit", binding, null, ppt, null);