Watermarks appear on document pages or on photographs as a means to protect copyrights. They can also be used to verify a document’s authenticity, as with paper currency. Watermarks were introduced as part of the paper manufacturing process in Italy in the late 13th century, when designs were added to paper stock while it was still wet pulp (hence the name, watermark). At that time, and for centuries to follow, watermarks were used to protect the paper itself against knock-offs; the watermark on a piece of paper identified the manufacturer, or the weight and quality of the parchment, or both.
While watermarks originated for use with printed documents, they can also be added to digital files, such as JPG photo files or PDF documents. In particular, watermarks are added to digital photographs as a way to prevent people from downloading and using those photographs without paying for rights to display them.
At Datalogics, we add watermarks to PDF documents produced by the free online demo programs we provide for evaluation of our products. This limits the ability of someone to distribute these PDF documents, and thus limits a prospect from using our free demos in their own production environment without paying for a license. If you have similar needs, we provide a means in Adobe PDF Library to securely add watermarks to the pages of PDF documents.
An important question to ask is, “How secure is the watermark I added to protect my document?” If you add a watermark to a PDF document and then the PDF document is printed, the answer is “quite secure.” The watermark can’t be changed once ink hits paper. But if you add a watermark to a PDF document and then send that document as an email attachment to your customers, or provide it for download from your website, you want to make sure that the watermark cannot be tampered with in that digital file. There are different methods to add watermarks to PDFs, and some are significantly more difficult to remove than others.
We recommend that you add your watermark directly to the page content. This method thoroughly bakes a watermark into the PDF document and is the strongest form of watermark security. That is the approach that we take with the new AddTextWatermark sample C++ program now provided with the Adobe PDF Library. This sample demonstrates how to securely add a text watermark to a PDF document. The watermark is embedded in the page structure of the PDF output file, and the saved file is encrypted, only offering view and print permission. The sample demonstrates how to set specified text, type style, font size, color, opacity, and scale the text to fill the page.
Note that while this sample is designed to add text as a watermark to PDF document pages, you can use this method, and this sample program, to add an image as a watermark as well. This will require more sophisticated coding effort, as you will need to add to your application the ability to convert common graphic formats into PDF images.
What’s interesting about this new sample watermark program is that we are actually returning to the original method we offered for adding watermarks to PDF documents. When we started selling the Adobe PDF Library in 1998, the sample program provided added watermarks using this secure method, directly applying them to the page content.
In August of 2015, we created a new set of sample programs for use with the Library, and included in that a new watermark sample program, AddWatermark, which showed how to add watermarks to PDF files as annotations. This was intended to demonstrate a more modern and intuitive approach, and it works fine if your documents are meant to be printed before distribution. But we’ve recently concluded that annotation-based watermarks do not provide sufficient protection if you plan to distribute digital files instead. An experienced PDF professional will likely be able to remove this form of watermark.
With that in mind, we are now including a new sample program with Adobe PDF Library that aims to combine the most secure method with easy-to-follow steps to help you apply tamper-proof watermarks to PDF documents. For a free trial of Adobe PDF Library, click here or contact us today!