Your problem is that you're trying to access the Word COM API from IIS. That is not a good practice. It makes desktop application Microsoft Word be present on your production server. Why on Earth should it be there? It's not good at all to call a desktop application from the server side code. Of course IIS forbids such stuff.
Instead you should find a library which doesn't depend on COM API. A good one (paid though) is the one made by
Aspose, in particular, you're interested in
Aspose.Words for .NET. I worked with it in an ASP.NET project. You can try to find some free libraries around.
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