Watermark PDFs

People used watermarks on paper in Italy as early as the thirteenth century to prove authenticity and discourage counterfeiting of administrative documents like postage stamps and currency. Paper manufacturers also use watermarks for branding.
The transparent effect is achieved by impressing a roll (called a “dandy roll”) with an embossed inscription or design on paper.
With the rise of electronic documents in the nineties, programmers wanted to replicate this helpful technique in the digital world. Andrew Tirkel and Charles Osborne created the expression “digital watermarking” in 1992 to present two methods to hide data in images.
There are many tools available so anyone can watermark audio, video, images, and of course PDF files.
Watermarking is one way to protect documents , along with encryption, digital signing, converting to PDF/A , and more.

You can add visible or invisible watermarks on electronic documents.
Static visible watermarks are showing regardless of who opens and processes the document. Their goal is to authenticate the document.
Dynamic watermarks can be visible or invisible, depending on settings. Furthermore, visibility can be enabled or disabled depending on the user and context. For instance, the watermark doesn't appear on the screen but is visible when printing the document to avoid sharing it physically with third parties.
A PDF watermark is a layer applied on top of visible content or in the background, behind existing content. Transparency can be set according to needs; the more transparent, the more invisible or less distracting it is.
Invisible watermarks embed information in a file in a digital pattern. They are more challenging to remove as visible ones because it is hard to remove something when you don't know where to look. This technique is used with audio and video files to identify pirated copies.
Invisible watermarks are not recommended for electronic documents because they can easily be bypassed by printing and rescanning or simply by saving the document in another color or format.

There are many different ways to protect and avoid falsifying an electronic document and its content.
We've just seen that visible digital watermarks help authenticate an electronic document. What is important here is the support of the message.
It is different than cryptography, which controls the access of the content of a document with a password, for instance. In this case, it is the message that is protected.
With steganography, from Greek steganós meaning "covered or concealed," and -graphia meaning "writing," the purpose differs slightly. Steganography aims to hide a secret message inside a banal document, so intelligence services often use it. In everyday context, the invisible watermarks we find in video and audio files for copyright or non-tampering purposes can also belong to this domain.