Files with .DOC extension represent documents generated by Microsoft Word or other word processing documents in binary file format. The extension was initially used for plain text documentation on several different operating systems. It can contain several different type of data such as images, formatted as well as plain text, graphs, charts, embedded objects, links, pages, page formatting, print settings and a lot others.
Files with XLS extension represent Excel Binary File Format. Such files can be created by Microsoft Excel as well as other similar spreadsheet programs such as OpenOffice Calc or Apple Numbers. File saved by Excel are known as Workbook where each workbook can have one or more worksheets. Data is stored and displayed to users in table format in worksheet and can span numeric values, text data, formulas, external data connections, images and charts.
You can also convert DOC into many other file formats. Please see the complete list below.