PDF document watermarking algorithm based on discarded page object

With the popularity of PDF documents, the security of a document becomes increasingly prominent. This paper presents a PDF document watermarking algorithm based on PDF document structure, where a watermarking signal is hided in the discarded page object. The algorithm can be resistant to some attacks, such as deleting words, adding words, deleting pages and pages rotation. The simulation results show that the algorithm is simple and the robustness is strong.