The Study Of The Digital Watermarking Algorithm Based On PDF Document

Recently, with the fast development of communication technology in computer network, both the new chances and challenges have been created for protection the digital information. With the superiority in the field of the copyright protection in multimedia and the authentication of media, the technology of digital watermarking is becoming one of the hot-spots. Achievements of digital watermarking have been concentrated on images, audio and video because they have been paid attention to. In fact, the paper document is more valuable than other digital medias. It is doubtless, no matter how change in transmitting way and media type, the role of transferring the human civilization and impelling the social advancement is played only by character. Therefore, It is important meaning, text is embedded the digital watermarking for protecting copyright, authenticating content and tracing operation.PDF format document has become a industry standard in the digital information era, and it has used widely in network for span-media, span-platform and safety. Because it is very important in the field of information, we need to study the digital watermarking based on PDF document quite.At present, in the field of digital watermark based on PDF document, there are two types of algorithm: one is based on text format; other is based on text content. There are some faults for these, for example, less embedding capability, worse concealment and so on. Thereby, with the problem of digital watermark in text, the article put the new algorithms forward. These algorithms include fragile watermark for content authentication, semi-fragile watermark based on document structure and robust watermark for copyright protection according to different use. Fragile watermark algorithm can prevent to alter any information in document, and is brought forward for multi-page and multi-object in document. Semi-fragile watermark can prevent to alter any information in text, and can find the position of alteration. Following the technique of image digital watermark, we can import the technique into PDF document, and the result is that good effect in copyrights protection and expression. Eventually, these algorithms are feasible in terms of theory and practice by proof of abundant experiment.