PDFStego is a tool that allows you to embed a hidden message in an innocent pdf file. Before embedding the hidden message, the application will first encrypt the message data with AES-128 GCM and then encode the encrypted data as base64. After embedding the encoded/encrpyted secret data in the pdf file, the pdf file will appear completely unchanged to the average, uninformed computer user.
While most PDF viewers won't render the hidden text, in the application's current state it's very easy to detect the presence of steganographic content. A tool for extracting text from pdf files is likely to expose the encrypted version of the secret message. If a secure password is used, the contents of your hidden messsage should still be safe as this will only expose the encrypted version of your message.
For example, if you have PoDoFo installed, the stego content can be detected with
$ podofotxtextract stego.pdf
For a more secure PDF steganography tool, I recommend checking out pdf_hide.
Install the PoDoFo library
$ sudo apt-get install libpodofo-dev
$ ./pdfstego -h PDFStego, Copyright (C) 2016 Aaron Gallagher This is free software, and you are welcome to redistribute it Usage: ::Embed:: ./pdfstego -e -c <coverfile> -m <messagefile> -s <stegofile> ::Extract:: ./pdfstego -x -s <stegofile> -m <messagefile>
3rd Party License Info
Base64 encoding/decoding is performed with base64.h from the project NibbleAndAHalf by William Sherif.
PDF parsing and editing is performed with the PoDoFo library.
PDFStego, Copyright (C) 2016 Aaron Gallagher This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. Contact: Aaron Gallagher <firstname.lastname@example.org>