If you find yourself with a need to protect confidential information and you’ve got a lot of PDF, then one such security option is the watermark. Watermarking your PDF document can signify whether the PDF document is a copy or an original, identify the owner or classify the document. The Muhimbi Microsoft Flow actions provides us with powerful watermarking engine that can be used to add watermarks to pages as well as adding headers, footers, page numbering and other recurring items.
Add Multiple Watermarks to PDF Document using Microsoft Flow
Clavin's Blog 