There are many kinds of files we can see in this modern life. In the past may be we only saw files with extension com or exe only as the system file. But the development in software created so many file types. The rule is still same because file extension must be created in three, combination of letter and number. What is your favorite file? I mean the most frequently you deal on your work may be. Mine is html file because I am web designer and programmer. This html file is file based on the language called Hypertext markup language. This is the standard of file used in the online website creation. There are other file types for creating your website such as PHP, ASP, JSP, CGI and many more. You only need to choose one or two languages you have mastered to build informative site for your client or for your personal use. How to know particular file opened with what software? We can use search engine to find this sensitive question. We need to do that because specific file only can be opened with specific program. When you type the file in the text field of the search engine and you press search, in less than seconds you will find the result.