1. Make the first field a text formfield. Use the Form toolbar. To get it, View > Toolbars > Forms.
2. After you insert the text formfield, right click it, and then select Properties.
3. Check "Calculate on exit".
4. The default name is Text1. Generally, it is a good idea to NOT accept defailt names, especially formfields. Formfields are named by the CURRENT order in the document. If text1 is moved and is now the second formfield in the document it is AUTOMATICALLY changed to Text2. This is withouit you doing anything. This is important, as....
5. Anywhere you want - literally anywhere, and as many times as you want - press Ctrl-F9. This makes curly brackets. You MUST press Ctrl-F9, as typing the curly brackets does NOT work. So press Ctrl-F9 and type "Text1", without the quotes.
6. Protect your document for forms. Tools > Protect document, and then select Forms, and press OK.
You are done. Everytime a user exits the first formfield, ALL other referencing fields are updated.
Gerry