what I want to do is forcing Windows to use my program as a base for creating thumbnail from some kind of files that are not images. In Windows you can see thumbnails from images, word documents, pdf etc - this is what i want with other file types. I can create bitmaps from this files (which later I want to use as a thumbnails) and store them somewhere. My question is how to connect extension with request of creating/checking if they exists thumbnail with my program and returning image/path to image. Any help and example will be very helpful.