Is there a way to suppress page numbers on the last 3 pages of a single document? I know I could make two separate documents but I need to submit a single file electronically for a class at university.

You should use section break, this way you can have two different sections in a document, go to page layout> breaks and select next page (the next page is the page that you want renumber and then go to insert>page number and then in the format deselect continuous from previous section, and in the start at place the page number that you want.

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.