A New Reversible Data Hiding Method in PDF Files for Secret Communication

Data hiding is a popular secret communication technique of recent times. Secret messages are embedded in a cover file and transmitted through the communication channel without raising any suspicion. Portable document files (PDF) are widely used due to their advantages, such as universal accessibility and platform independence. However, data hiding techniques in PDFs often encounter such problems as visual distortion and undesirable increases in file size. This study proposes a more effective and practical approach for hiding data in PDF files by increasing the hidden data capacity while minimizing file size growth. In the proposed method, data is embedded by appending it to the end of TJ operators used during the text rendering process in PDF files, without altering the original visual and structural integrity of the document. Furthermore, thanks to the reversible nature of the method, the embedded data can be accurately extracted under proper access control, and the original PDF file can be fully restored. Experimental results demonstrate that the proposed approach offers high embedding capacity and minimal file size increase, providing significant advantages in applications such as secure communication and copyright protection. These findings indicate that the developed method outperforms existing techniques and is well-suited for practical use.