Word does dynamically expand a document as the user types. It does not really have pages until print time, it has a flow of text. It does have all the pages you want to use.

You can use the RAND autocorrect function or its relative LOREM to fill a document with dummy text. See the random text Add-In.

Are you trying to create something to be filled in by hand? What is your purpose in creating multiple blank pages? If you tell us that, someone can probably tell you how to accomplish what you want.