If you’re a Mac user and you share Microsoft Office documents with PC users then you need to make sure that the file extension is included when you a save a file. A file extension is typically a three letter code that appears at the end of a file name and is used by the Windows operating system to identify which program should open a file (i.e., .doc for Word, .ppt for PowerPoint). With Microsoft Office for Mac OSX, appending a file extension is optional; if you’re using a Mac you should check to see if your Word document or PowerPoint presentation includes an extension before posting it to Blackboard or emailing it to your colleague. For example, a Word document would contain the file name followed by the extension as in “MyDocument.doc.”
When a PC user tries to open file with a missing extension, he or she will usually encounter a message stating that Windows cannot open the file. Mac users can prevent this problem by verifying that the Append file extension box is checked in Microsoft Office programs (Word, PowerPoint, and Excel).
Append File Extension in Microsoft Office
When you save your document, File < Save As, check the Append file extension box, if it is unchecked. Once you check the box, the file extension will be automatically appended each time you save.
Tip for PC users
If you receive a file without an extension and you know which program was used to create the file, then you can try opening the file from the program. For a Word document, you would open Word then select the File menu and click Open. In the pull down menu next to Files of Type, make sure that All Files (*.*) is selected from the pull-down menu. Select the file from its saved location and click Open.