Bitar, A. W., Darazi, R., Couchot, J.-F., & Couturier, R. (2017). Blind digital watermarking in PDF documents using Spread Transform Dither Modulation. Multimedia Tools and Applications, 76(1), 143-161. https://doi.org/10.1007/s11042-015-3034-2 (Original work published 2017)