If the error is unknown file format then the file is not a Word file or it is corrupted. If you cannot sort it out, attach the file to the post and I will have a look.
Not all .DOC files are Word files. It can be Word for DOS or Word Perfect file for example which is opened in MS Word fine because it silently converts it, yet Aspose.Word will throw unknown file format to this file.
Sorry for the delay, but the file you emailed me works fine with Aspose.Word. I can open and save it fine with just new Document(fileName);
Lets take it slowly step by step. Please make sure you are using latest Aspose.Word. If you still have a problem, please specify what exactly is your code doing and what exactly is the error message.