.exe
The source files used to install office. They are usually on CD/DVD or a network share.
The MSBACKUP program in DOS receives its settings from the setup file. This setup file features a .set extension and is created after you make file selections and configure backup settings.
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An image file. It is a Microsoft bitmap file. You can open it in almost any image editor or viewer
MPEG-4 audio files can be imported to iTunes 9. They will usually have the extension .m4a or .mp4. The AAC files that you can purchase from the iTunes store are MPEG-4 audio files.
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There is list of programs that support DO file extension http://www.howopen.org/en/extensions/web-files/do
RealPlayer video files usually have one of the following extensions: # .rm # .ram # .rmvb
.XLS files are standard Microsoft Excel spreadsheet files. .XLT extension is used for the Excel template files. - Neeraj Sharma
MUS extension files are usually associated with music files used for training or composing on your PC. They can be created by using several different types of programs which deal with professional music composition, such as Finale, Sibelius or Melody assistant. This type of file is not usually able to be played in standard media players since the file with this extension will contain specific information regarding the music file, such as tempo or tone.. Incorrect associations are the cause of many file extension errors.
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...