Reversible data hiding in PDF document exploiting prefix zeros in glyph coordinates

In the contemporary world of information technology, PDF (Portable Document Format) has become the de facto document standard which allows users to exchange and view electronic documents across various platforms. PDF is the most widely exchanged document format since Internet gained popularity. Although PDF has a good authenticity system by making use of digital signatures, the file format is still susceptible to copyright infringement as there are many libraries available on the Internet to bypass the digital signature of a PDF. Therefore, claiming ownership for PDF has become a paramount issue that needs to be addressed. This paper proposes the idea of hiding data in the glyph positioning coordinate value. To suppress bit stream size increment, the reverse zero-run length coding technique is adopted. Experiments are conducted to verify the basic performance of the proposed data hiding method. In the best case scenario, 0.62 bits of data can be embedded into each Byte of the PDF file. The injected leading zeros can be removed to restore the original PDF file.