One assumes you want to restrict the uploaded file types to a certian set - eg doc, docx, pdf.. whatever. So I would think it possible to examine the uploaded file/s (byte by byte) in the code-behind to at least check that its format is that of the supposed file type, according to its extension. Some research would be required to determine a reasonable test for each type, but I wouldn't have thought that that would be beyond the wit of man... or woman.