Displaying Field Results Correctly
When you first insert a field code into a document, or when you create a new document with a field code in it, Word calculates the value of the field code and displays its results.
After the first time, however, field codes are never updated automatically, except when a file is opened. So, for example, if you create a new letter based on a template that has a {Date} field code, Word puts the current date in the new document. When you close and reopen the document, Word updates the field if necessary, but if you leave the document open overnight, the date won't change.
When you open a document containing a field, the field is updated automatically. There are two common ways to update a field manually—that is, to have Word recalculate the field's value and display the new value in your document:
Select the field, and then press F9.
Select one or more fields, right-click, and choose Update Field.
You can also specify that Word should automatically update all fields in a document immediately before printing the document. To set this option, choose Tools, Options; click the Print tab; and check the Update Fields box. The setting is global, so it stays in effect for all documents until you change it.
You can permanently eliminate a field, and have it replaced with the text that's currently showing in the document. For example, if you've written a letter by using a {Date} field, you might want to replace the field with its results, so when you open the letter later, you'll see the date you sent the letter rather than the current date. This process is called "unlinking" a field, although it actually removes the field entirely, replacing it with the current value of the field.
For example, a purchase order might include a bookmark called DollarAmount, where the user enters the price of an item. Later in the document, you might refer to that number in check format, using a field like this:
{= {REF DollarAmount} * dollartext * upper}
If the amount the user enters is 79.82, the field code result appears in the document as
SEVENTY-NINE AND 82/100
When you unlink the field, Word eliminates the field code entirely, replacing it with text that you can edit directly. Later, if you change the amount in the DollarAmount bookmark, the text won't change.
To unlink a field, do the following:
If you want to be certain the field result is current, update the field. (In some circumstances, you might choose not to update the field; for example, if it shows an old date and time that you want to preserve.)
Click to position the insertion point in the field. It doesn't matter whether field codes or field code results are showing.
Tip from 
If you regularly work with fields, add an Unlink Fields button to a convenient toolbar, using the procedures described in Chapter 2, "Customizing the Office Interface."
To lock a field—that is, to prevent a field from being updated—select the field or place the insertion point in it and press Ctrl+F11. To allow the field to be updated again, select the field and press Shift+Ctrl+F11.