23. The watermark detecting method according to claim 20 , wherein said obtaining the layout information further comprises dividing said document into a plurality of segments.
23. The watermark detecting method according to claim 20 , wherein said obtaining the layout information further comprises dividing said document into a plurality of segments. 24. The watermark detecting method according to claim 23 , wherein said extracting the secret message sequence further comprising extracting each secret message of said secret message sequence based on inter-word space changes in the corresponding segment indicated by each of the calculated embedded positions, respectively.