How can you enter extended ASCII characters into a document using a keyboard?

To enter extended ASCII characters using a keyboard, you can hold down the "Alt" key and type the corresponding numerical code on the numeric keypad. For example, pressing "Alt" + "128" will produce the character "€" (Euro sign). Make sure the Num Lock is enabled for this to work. Alternatively, you can use character map tools available in your operating system to copy and paste the desired characters.