Digital Watermarking for PDF Document Authentication
Zhang Chun · Journal of Tianjin University Science and Technology · 2003
The growth of networked multimedia systems has brought many advantages in the creation and distribution of digital works. The transparence of data and the ease of manipulating also facilitates unauthorized use, misappropriation and misrepresentation. In this paper, a digital watermarking algorithm is proposed for PDF (Portable Document Format) document authentication, based on a detailed analysis of PDF operators with reference to page description. The watermark, with the features of the PDF character codes, is embedded into the document by modifying the character spaces. The authenticity of a PDF document can be verified by comparing the watermark with the features of character codes. The experimental results demonstrate that the watermarked PDF document possesses good perceptual transparence, and that the proposed algorithm can detect any character change at the PDF document at the block level.