I take it you want a page number on page 3.
You do not want a page number on page 1 or 2.


In your footer place the following field.
{ IF { PAGE } = 3 3 }
00 deleteme 1.png

This will only print a number on page 3. If you wanted it to say "Page 3" you would use the following instead:
{ IF { PAGE } = 3 "Page 3" }


You can't simply type this. The { } field delimiters must be inserted by Word using Ctrl+F9.


IF Field