How to add watermark to a PDF: non-removable & dynamic security

  What is a watermarked PDF?

A watermarked PDF is a PDF that has a text and/or image watermark added to it which is displayed when the document is viewed and/or printed.

Text watermarks may be static (“This document is the property of ABC Corp.”), or dynamic (“This document was viewed by Joe Bloggs joebloggs@acme.com on 04/08/2021”).  In dynamic watermarks, the text is automatically updated with the system/user information at the time of opening or printing.

Watermarks are added as a layer to the PDF (which is why they are easy to add) and can be made to appear on top of or behind existing document content.

PDF watermarking is able to emulate many of the subtleties of the physical world.  If you think of a banknote, some watermarks seem inside the paper whilst others are on top.  You can get a similar effect with PDF watermarks.

Think of the information being printed as if it were in layers, rather like a sandwich.  The content sits in the middle, and the PDF watermarking can be over content, or under content, or both.  Also, the PDF watermark can be set to be lighter or darker than the content.  This lets the watermark ‘blend’ with the content so that it has a more seamless presentation and is less distracting, if that’s what you desire.

Applying PDF watermarking takes a certain amount of discipline and artistic judgement, then. It is not necessarily a mechanical process of having a ‘bog standard’ graphic and/or text and applying it to every document that goes out.

  What is the point of watermarked PDF files – why add watermarks to a PDF?

One way to improve the security of your PDF documents is to add a watermark to them – see also Using Document Watermarks as a copying deterrent.

Watermarks can be used in several ways:

1. to resist falsification
2. as a copying deterrent
3. to display classification
4. to specify the document is not an original
5. to link the document with a specific authorised user
6. to establish who the owner is

Using watermarks to resist falsification

When using watermarks to resist falsification, PDF watermarking is used in exactly the same way as watermarks on banknotes or cheques.  If you try to make a fake it can be made very difficult to exactly copy the PDF watermark, so anyone seeing the document will also see that it is a fake.  This use of PDF watermarking can be very important where official documents have to be printed/printable and must be demonstrated to be authentic.  (This is how you know a 20-dollar bill or a ten-pound note is genuine.  It doesn’t mean documents can’t be faked.  There are still fake banknotes doing the rounds and one pound coin in 36 is a fake.  But PDF watermarking is significantly better than doing nothing.)

Using watermarks as a copying deterrent

This might include text such as ‘It is illegal to copy content from this document’, and/or by using dynamic watermarking to display user information so that users are discouraged from giving copies to others.

Using watermarks to display classification

This is the method of classifying documents by adding a watermark to them that displays how the document should be treated.  For example, adding a confidential watermark or a ‘top secret’ watermark as a stamp or text.

Using watermarks to identify the document as an original or copy

This is achieved by adding a stamp or text to a PDF document to mark it appropriately.  For example you might watermark a PDF with “copy” before printing and/or when it is viewed.

Using watermarks to link a user to a document

PDF watermarking is a useful way to link an identity to a document.  The PDF watermark may be something as simple as a unique number that is associated with the authorized user of a document, or it may be their name, email address, company name and so on.  The point of this PDF watermark is to make it clear who the source of the document is if it is not intended to be copied and passed around.  This technique has been in use for a long time to identify the source of documents ‘leaked’ to the press or who it was obtained from by IPR pirates.  The PDF watermark works because the source of the information (whether a leaked or pirated document) usually does not want to be linked to it.  This does mean that when using PDF watermarking in this way you need to have a clear link between the identity on the document and the identity of the entity that it was authorized to.

Using watermarks to establish ownership

The owner of the document may be different to the document Publisher.  If for example a reseller has been given permission to sell a book, report, etc. then they might want to add a PDF watermark that establishes them as the authorized reseller.

  PDF print watermarks – add print only watermark to PDF files

The most common reason why people want to add watermarks only when the PDF file is printed (i.e. no watermark is displayed when the document is viewed) is to prevent printed copies from being easily re-distributed.

The best way to discourage this is for the watermark to display user identifiable information (such as the user’s name, email, etc.).  This can easily be achieved by using dynamic watermarks where user information is automatically inserted when the PDF document is printed.

Locklizard supports dynamic watermarks and enables you to apply a PDF watermark only when printed, only when viewed, or both.

  Watermarks for confidential documents: why add a confidential watermark to a PDF?

Many companies need to distribute confidential PDF documents to selected users or third parties but do not wish them to be distributed any further.  As a security measure (and sometimes for classification) they add a confidential watermark to PDF documents (the same as a confidential watermark stamp on paper documents) on the basis that they will be honored.

However, in reality adding a confidential watermark to a PDF document provides zero protection since it is meaningless.  It does not stop PDFs from being shared with others.  The confidential watermark can also be easily removed in any PDF editor.

If you want PDFs to remain confidential then adding a confidential watermark will have no benefit unless you have other PDF security measures in place to make the watermark protected in the PDF and prevent document sharing.

Confidential image watermarks

Locklizard provide our Publisher customers with a range of confidential image watermarks which they can use to add a confidential watermark to PDFs.  Confidential image watermark examples are below:

  Does adding a watermark to a PDF make it more secure?

If the watermarked document contains the recipient name, and it cannot be removed, then yes, it does make it more secure.

If you use Adobe Acrobat or a similar PDF editor to add a watermark to a PDF document then that does not make it any more secure.  The reason for this is because users can easily remove the watermark even if the file is password protected.  See Removing PDF watermarks.  This is true of all password protected PDFs that have a watermark applied to them and includes secure data room systems that enable users to download watermarked PDF files such as Digify and DocSend.

If you want to add a watermark that cannot be removed then you need to use PDF DRM software that adds watermarks to PDFs that cannot be removed using PDF editing software.

  Invisible watermarks & social DRM: Worth using?

In a bid to stop users from removing PDF watermarks, some DRM providers had a seemingly bright idea: what if, as well as displaying the watermark on the document, they hid them in the document’s code?  Unique identifiers would be applied to each document so that when they are published online the publishers can track down who shared them.

It’s not a terrible idea, but it’s not very effective at preventing document sharing in practice.  Watermarks are primarily used as a deterrent, and it’s hard to deter a user with a watermark they can’t see.  Sure, you can track them down afterward, but at that point, the damage is already done.

If the user does know about the hidden watermarks, they can simply remove them.  Most social DRM / hidden watermark solutions don’t use any encryption or DRM, so the code is visible and editable.  All the user has to do is find the “invisible” watermarks and delete them.  Granted, this is more time-consuming than removing Adobe protection, but it’s still not going to stop a determined party from leaking your document.