The interop library is slow and needs MS Office installed. Many times you don't want to install MS Office on servers.
I'd like to use Apache POI, but I'm on .NET.
I need only to extract the text portion of the files, not creating nor "storing information" in Office files.
I need to tell you that I've got a very large document library, and I can't convert it to newer XML files.
I don't want to write a parser for the binaries files. A library like Apache POI does this for us. Unfortunately, it is only for the Java platform. Maybe I should consider writing this application in Java.
I am still not finding an open source alternative to POI in .NET, I think I'll write my own application in Java.