A new covert communication method via PDF files is proposed. A secret message, after being encoded by a special ASCII code and embedded at between-word and between-character locations in the text of a PDF file, becomes invisible in the window of a common PDF reader, creating a steganographic effect for secret transmission through the PDF file. Experimental results show the feasibility of the proposed method. (C) 2009 Elsevier B.V. All rights reserved.
