What file extension do all Microsoft word processors read?

RTF is the lowest common denominator, but it also has the fewest features. You can also probably get away with saving it as a .doc. If your school has Office 2007 or 2010, then you can use docx.

.docx can be only read by 2007 and 2010 versions. .doc can be read by all versions

All word processors know Rich Text Format (.rtf). As the name implies, the format is fine for text but not for other things you commonly find in word processing documents such as pictures, tables of contents, captions, and page layout. All versions of Microsoft Word can open and work with the old proprietary Word binary format (.doc). Starting with Word 2007, the binary format was deprecated (fancy word to say made obsolete) due to pressure from open source advocates. Starting in 2007 Microsoft and most other up-to-date word processors use the international open standard for word processing documents (.docx). Unfortunately, many software companies have been dragging their feet in adopting the international standard, mainly because they don't want to pay their programmers to bring their products up to date.

Another option is to save as .rtf which stands for Rich Text Format. All word processors should be able to read it. NOTE: Not to be confused with Rich Text Format in Microsoft Outlook, and emails sent in that format are unable to be read by ANY other email program, including Microsoft's other major (and free) email program, Outlook Express.

save it as ".doc" (MS Word-97 to 2003)