In Word 2016 at least, from a blank document, press control+enter to add a second page. Then add page numbers (alt+n, n, u then any style - top of page, plain text 1 is fine). Press the applications key and choose "format page numbers", press down arrow to change number format to - 1 -, - 2 -, - 3 - and press enter to accept.

Page 1's number reads as "- 1 -" but page 2 onwards only read as "dash".