The only thing that willl happen is that the file will be associated with a different application program, however, the data (and file type) will still remain the same. For instance if you took a JPEG photo and changed the file extension from .jpg to .doc it would become associated with MS Word and prompt MS Word to launch if you double clicked on the file.
But when word comes up, it will give you an error stating that its not an acceptable file type. If you took that same file and attempted to open it in a graphical editing program such as Photoshop, even though it has the .doc extension it will still come up without a problem.
You can change programs formats by naming the way lets say a program is answers.exe just change the extension to Answers.dll or Answers.html.But the files which use EXE extension works with exe only.Many time you are asked to change the files extension from zip to mp3 to download a Song.At that time just change song.zip to song.mp3 and change the file type to 'all files'.
sai
There is list of programs that support DO file extension http://www.howopen.org/en/extensions/web-files/do
.XLS files are standard Microsoft Excel spreadsheet files. .XLT extension is used for the Excel template files. - Neeraj Sharma
Picture files no matter name they have they will definitely have an extension like xx.jpg . bmp and may more. window automatically will search for these files extension if asked to do so.
.b is an extension for binary files mostly used by video game emulators... .b is also the extension for BASIC programming language source text files...
msc
.fla
.exe
A compiled Help File in Windows will have the extension .chp
An applet is a Java application, this saves files in a .class extension
JAR files are simply ZIP files with a different extension. Just chnage the extension from .zip to .jar.