Step 1: click Tools menu > click Options
Step 2: click View tab, check the Field codes in Show group to display the field codes in document.
Display or hide field codes in Word 2007/2010/2013
Step 1: in Word 2007, click Office icon 
, and then click Word Options;
, and then click Word Options;
in Word 2010/2013, click File tab 
, and then click Options.
, and then click Options.
Step 2: click Advanced, and then check Show field codes instead of their values to display field code in document.
