If you want to know the file formats supported by any API, you can click Learn More button against each API at http://www.aspose.com/.net/total-component.aspx and check the file formats supported by each API.
If you want to just detect the format of a file, you can use FileFormatUtil.DetectFileFormat method from Aspose.Word, Aspose.Slides and Aspose.Cells etc. to detect file format. In fact Aspose.Cells method can detect more file formats as compared to other APIs as you can see at http://www.aspose.com/docs/display/cellsnet/Aspose.Cells.FileFormatType+Enumeration
Unknown format will be returned if file is not recognized by any API.