On the Find tab there is a check box for "Highlight all items found in" and
choose Main Document. This will "select" all the occurrences of the Find
criteria, once pressed the Find All button Word will tell you the number of
occurrences.
Close the window and these occurrences will be "highlighted" for an action,
such as a change in style.
The Replace function can also be used to Replace all occrrences of a Find
Criteria and and the Replace All will do the necessary change
"simultaneously".
Can you provide further detail of what you are trying to do and how you are
trying to do it, please. We may them be able to help you with more pertinent
information.
Regards
DeanH