In Microsoft Windows, file names can contain some punctuation characters, such as commas or periods. When you save a file with a name that ends with a period — for example, Sales. — Microsoft Office programs add another period and the default extension to the file name. For example, a Microsoft Word document saved as Sales. will appear as Sales..doc. When you save a file with its default extension, it isn't necessary to type a period following the file name. Office programs automatically add the period when they add the extension.