A family of Microsoft word processing software products for creating web, email, and print documents.
As Cindy has pointed out, your printer is responsible for the nonprinting border. But let me point out another misconception: you should not set your margins to 0". This will make the letterhead unusable for text in the document body. Instead, set the margins as desired for the letter itself, with sensible side, top, bottom, and header/footer margins. Then enable "Different first page" and insert your letterhead graphics in the First Page Header/Footer. Set the wrapping to Square or Behind Text and the position to Left and Top/Bottom relative to Page. This will allow the graphics to extend to the edge of the page (though they still won't be printed completely), and they will not move if the margins are changed.