Special characters such as umlauts, trademark symbols, fractions, and open and close quotation marks do not appear on most keyboards. When you want to use a special character, you either must insert them by entering their code on the numeric keypad or by using the program called Character Map that comes with Windows. (See Windows' help for more information.)
Although most fonts contain a complete set of special characters, some fonts do not. For example, if you are using a font that does not contain the special symbol "µ," you must change to a font that does contain it in order to insert that object.
Each character in a font is associated with a number. For example, "µ" has the number 0181, regardless of the font. The number is called an ANSI (American National Standards Institute) character code.
Text fonts use the standard ANSI character codes. Non-text fonts such as dingbats are assigned character codes, but there is no standard. You must use either the keypad or the Windows Character Map to insert non-text characters.