The formatted citations and bibliography in your document are not plain text; they contain hidden data that make it possible for EndNote to unformat and reformat citations and bibliographies.
Formatted citations and bibliographies in Word documents are Microsoft Word fields. This gives EndNote the ability to uniquely identify them.
When you click on a field in Word (such as a formatted EndNote citation or the bibliography), it becomes shaded. You can change this behavior so that the fields are always shaded, shaded only when selected, or never shaded. To do so, select Options from Word’s Tools menu and select the View option. There you will see the options for field shading. Click the Office icon in the top left corner of Word, click Word Options, then click Advanced, and scroll down to "Show document content" to find field shading options. Preferencesfrom the Word menu and select the View item to see the options for field shading.