This paper presents a traitor-tracing technique based on the watermarking of digital documents (\pdf{} files in particular). The watermarking algorithm uses a chain of three separate techniques that work in synergy. The embedded payload can withstand a wide range of attacks and cannot be removed without invalidating the credibility of the document. We will present an implementation of the approach and discuss its limitations with respect to documents that can be watermarked and quality of the watermarked documents. We will also analyse two payload alternatives and how the encryption scheme may alleviate the chilling effect on whistle-blowing.