Internal Links become invalid after adding watermark

Hi, I’ve tried to use the plugin to add watermark in my ebook.
But after some testing, I found that the internal links all became invalid. Is there any reason behind this?

By the way, is it possible to use my encrypted pdf to add watermarks?
Cus I’ve tried to use that but it showed “unable to add watermarks.”

Thank you.

Sincerely,
Nora

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