VBA code to add watermark in all pages

[Guessed]

A simple concept like a watermark is WAY more complicated than it should be because:
1. A watermark is a floating graphic stored in a header (or footer)
2. Each section can have up to three different headers
3. Each document could have a very large number of sections
4. Some headers are linked to (copies of) previous sections and some aren't
5. Floating graphics can be placed in any header of any section but VBA treats them as if they are stored only in Section 1's headers.
6. Adding watermarks over the top of other watermarks is bad so any complete macro solution needs to be able to identify and remove existing watermarks too.

Microsoft added the Design > Watermark functionality to Word around about v2007+ and this works well on simple documents (without too many section breaks and changes to page setups). However it falls down somewhat when document sections get complicated.

Code that puts in Watermarks is pretty time-consuming to create if it needs to deal with all the above issues. It can be done, but code like that is rarely spotted outside of paid jobs since the effort required is usually greater than the goodwill required to create it and then give it away for free.