Watermark On Pdf can add watermarks to all or some pages of a PDF file. If you then secure the document with a password to prevent changes, it can't be removed
Here are some reasons you might want to enable watermarking of PDF documents: Watermarking prevents copying, changing, or tampering with the original document. It would help in preserving content that needs to be protected in a document, such as sensitive or confidential information. It may help in displaying a document (or part of it) in a browser, for example when sharing the document as part of a web page or within a file containing other pages. Watermarking provides greater control over your documents. For example, watermarks allow you to include additional metadata on the page, such as the image you want to display, date and time to display, or more. Watermarking can be applied to text, images, and other file types. You can make the watermark remain in a visible manner when the document is displayed as part of a web page. For example, in a PDF file, the watermark would remain when you changed.