When I print a document out it looks different on paper to how it looks on screen and in print preview. Why is this? and what can I do about it?

This is usually caused by the document being typed in a non True Type font. Looking at the list of available fonts in Word

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You can see that the fonts Letter Gothic, LinePrinter, and Marigold all have a different symbol next to their name than the others showing on the list. The fonts with a TT symbol next to their name are the True Type fonts.

These will always look exactly the same on paper as they do on the screen. The fonts with the little printer symbol next to them tell Word to use the fonts that are built in to the printer. Consequently there is no guarantee that they will look the same on paper as they do on the screen.