When you're designing documents for the Web, there are Internet conventions with which you should be familiar. This document provides information about these conventions and offers recommendations from Adobe Technical Support to help you avoid some of the common pitfalls of Web-document design. Using Filenames Correctly Your Web documents must be named according to Web-naming conventions for Web browsers to display them correctly. All files for the Web must have a filename extension, which is a suffix consisting of a period followed by one or more characters. For example, Web page documents usually have the extension .html or .htm, GIF images usually have the extension .gif, and JPEG images have the extension .jpg.
Filename extensions tell a Web browser how to interpret the file type.
When you're creating your documents, make sure each of your files has the appropriate filename extension so links to the documents will work. To be safe, use only letters, numbers, hyphens only after the first character, and underscores in file and folder names. JPEG images should be in RGB format. Keep this in mind when you're creating your documents. Naming Your Home Page Your home page is the first document users see when they visit your site.