Question

How are pages watermarked such that they can be visible only by pointing it towards a light source e.g. NCERT books?
I only want to know the printing process behind it. Not how publishers manage to add such a watermark in the soft copy of a page/book.
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Answer 1

Answer:

Security watermarks are designed to be invisible, or functionally out of the way, on original documents and to show up on copies of the original documents. Since most such watermarks rely on either super-fine printing technology or special security paper, the options available within Microsoft Word are limited, but it is possible.