To amend the defects of low perceptual transparency, low capacity, low security of the present information hiding technology in PDF files, we present a novel steganographic algorithm which is better in perceptual transparency property, capacity and security. Attributive to the insensitiveness of PDF files to the seriation of entries, the algorithm helps to realize the information hiding in high degree of perceptual transparency and in large capacity without writing new data in the original file. And as the initial value of the chaotic map, the key is generated by applying the secure hash algorithm, to keep the system meet Kerckhoffs rules and enable integrity service. In addition, this algorithm is equipped strong anti-statistical attack ability.