Filename Extensions A-go-go What is a filename extension? your computer. The problem A filename extension is usu- comes when you send those ally three letters at the end of a files to another computer. file name that indicates what program created the file. For What if there’s no extension? example, files created by Mi- When you send a file to an- crosoft Word have filenames other person, if there is no file- that end in “.doc”. For example, name extension, there is a good if you see a file called chance that the other person’s “final.doc”, it is a Word docu- computer will not be able to ment. To open it, you will need read it. Before Word or an- sharing a file, Common other pro- make sure that gram that can For more information it has the cor- Extensions open Word on filename extensions, rect filename documents, search “Filename exten- extension by .doc = MS Word such as sion at: renaming the .xls = MS Excel Pages, http://en.wikipedia.org/ file in the Finder .ppt = MS Powerpoint OpenWord, or resaving it .pdf = Portable Docu- or TextEdit. from the original ment Format application with the “Hide Ex- Do I have to add extensions .isf = Inspiration tension” box unchecked. myself? .html = Web pages If you receive a file with no Most of the time, the pro- .mp3 = Audio file gram that you are using will add extension and your computer .jpg = picture extensions for you. When you doesn’t know the file type, the .mov = Quicktime Movie save a document, you can let icon will probably be a blank your computer know whether or white rectangle. Let’s say you .wav = Audio file not you want to see extensions got a file like this and thought it on your filenames by using the was probably an Excel spread- checkbox shown here: sheet. Open Excel, go to Even if you don’t add an ex- File>Open, and select the file. If Excel can open it, you were right. If Excel says that it cannot open it because it is an un- tension, your computer will known file type, try another know what application to use program or ask the person who for any documents created on sent you the file..