The reason this happens is that Word uses information from the active printer driver to optimise the page layout. Simply changing drivers on your own computer (either so you can use a different printer or even - in rare cases - just because the printer manufacturer decides to update the drivers for your existing printer) could have the same effect.

If you need to ensure your colleague sees exactly what you do, send a PDF of the document.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]