This code is part of 2 dimentional code family, it's in fact a code with several rows which can encode up to 2700 bytes what explain its name of "Portable Document File". The encoding is done in two stages : first the datas are converted to "codeword" (High level encoding) then those are converted to bars and spaces patterns. (Low level encoding) Moreover an error correction system with several levels is included, it allows to reconstitute badly printed, erased, fuzzy or torn off datas. In the continuation of this talk, the word "codeword" will be shortened into CW.