There are at least two ways, the easiest of which is to create a new section to start the first of those last three pages and edit the header or footer containing the page number. First uncheck "link to previous" then delete the page number. See Sections / Headers and Footers 2007.

A second way is to set your page field to only display on pages except the last three. See How to Control Page Numbering in a Word Document.

{ IF {PAGE} < { = { NUMPAGES } - 2 } "{ PAGE }" "" }
The braces {} must be inserted by Word in pairs using Ctrl-F9, you cannot type them in.