The name of every file you upload into WebCT needs an extension. An extension is a dot (.) followed by a few letters at the end of a file name. The extension identifies the type of file. For example, a file named "syllabus.doc" is a Microsoft Word document; "syllabus.html" is a Web page. Normally, Mac OS X hides extensions--they are there, you just can't see them. But you can make the extensions visible:
You can also show extensions when you save a document in some applications.