Sizes in Word are in Points (there are 72 points in an inch)

You can use a function to convert cm to units Word understands
.Height = CentimetersToPoints(5.11)
.Width = CentimetersToPoints(20.96)

Bringing in the graphic as an inline shape is somewhat problematic. What if the user doesn't have S drive mapped the same way? I see your preferred width is the same as an A4 page so I assume you were expecting the graphic to start at the top left of the page - you wont get this with an inline shape unless the header space is zero and then the users will get nagged about margins when printing. Are you confident the left margin is always the same in these docs?

FWIW, I would be doing this a different way. I like to save the headers and footers as building blocks in the template itself and then replace the header with that building block.

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Andrew Lockton
Chrysalis Design, Melbourne Australia