I have a javascript code like this:
o = new ActiveXObject("ASDFsome.Application");
utilites = WScript.CreateObject("ASDF.Utilites.UTF.Converter")
utilites.Convert(outFile, xmlProp.xml)
Now I want to rewrite it in C# code. How should I use ActiveXObject in Net?
Answer
This is in no small part why the dynamic keyword was added to C# version 4:
dynamic utilites = Activator.CreateInstance(Type.GetTypeFromProgID("ASDF.Utilites.UTF.Converter"));
utilites.Convert(outFile, xmlProp.xml);
If you're stuck on an earlier version then using a VB.NET class library is the best approach. It directly supports the CreateObject() function as used in your scripting code.
Last but not least, unlike the scripting language you've been using, both C# and VB.NET support early binding. That starts by adding a reference to the type library, Project + Add Reference and use either the COM tab or the Browse tab to pick the .tlb or .dll file that contains the type library. You might not have one if the component was designed to be only ever used from late binding scripting languages. We can't otherwise help you find the proper type library, the vendor or author would know.
Really last but not least, this smells like a utility that knows how to read a utf-8 encoded XML file. That's already really well supported in .NET with the System.Xml namespace.