HTTP is not a file, it is a protocol. It therefore does not have an extension. If you mean HTML files, which are web pages, then either htm or html can be used as extensions.
http://filext.com/file-extension/PRJ
There is list of programs that support DO file extension http://www.howopen.org/en/extensions/web-files/do
For individuals and families, the tax extension deadline is October 15, which gives you a 6 month extension of time to file your taxes from the April 15 tax deadline. You can file your extension online with an e-file provider like FileLater (http://filelater.com).
Here is some information on how to file a tax extension: http://taxes.about.com/od/preparingyourtaxes/ht/FileExtension.htm. Form 4868 should allow you to file an extension for up to 6 months after the original deadline.
According to FileInfo.net, it is a Korg Instrument Bank File. http://www.fileinfo.net/extension/pcg
What is the file extension What is the file extension
Automation file synchronization over LAN and WAN, FTP, HTTP, SMTP, POP3, PING. File
The most common .dat files are video files from a video cd. Try playing with media player. See this also http://filext.com/file-extension/dat
file extension for video is 101
.html, .php, or .htm
The file extension tells about the type of file, with the extension three letters. For Eg:- *.txt -- text file *.exe-- executable file
file extension