The way Word works is that you can position graphics inline or floating (text wrapping). I nearly always prefer inline as the file size is minimised and the graphic flows logically with the text. However that won't allow you to maintain the position of the graphic at the bottom of the page OR the top of the next one. To do that you would need to turn on the text wrapping for the graphic.

With text wrapping you can position a graphic 'always' at the top of a page OR 'always' at the bottom of a page but not do both. Whichever one you choose, the graphic will be anchored to a particular paragraph on that page. If that anchor paragraph moves to the next page then the graphic does too. The graphic can be positioned relative to the anchor paragraph OR relative to the page where the anchor paragraph is located.

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Andrew Lockton
Chrysalis Design, Melbourne Australia