  We propose different approaches of PDF files based steganography, essentially
based on the Chinese Remainder Theorem. Here, after a cover PDF document has
been released from unnecessary A0, a secret message is hidden in it using one
of the proposed approaches, making it invisible to common PDF readers, and the
file is then transmitted through a non-secure communication channel. Where each
of our methods, ensure the condition that the number of inserted A0 is less
than the number of characters of the secret message s.
