Important printed documents such as certificates, insurance policy, and other important documents can be manipulated by someone according to the technology development. In this study, we propose a technique on document authentication using watermarking. The image which has a copyright sign (copyright image) is embedded to the cover image such as logo or any other image to be watermarked image, then the watermarked image will be embedded on document, the watermarked image will be extracted when the document will be authenticated. The method is based on DCT (Discrete Cosine Transform) algorithm. The copyright image which has embedded on the cover image either on 24- bit grayscale images or 24-bit color images are detected through print-scan process, although grayscale 24-bit cover image is better than color 24-bit cover image. It shows that the technique is efficient for document authentication. A printer which is used for this technique to be very influential on the quality of the printed document and it will be influenced on extraction process, the laser printer is recommended than inkjet printer. The next future work is expected that the 24-bit color image is able to be extracted as well as the 24- bit grayscale image.