The widespread replacement of cellulose paper with polypropylene (PP)-based synthetic paper has been hindered by the relatively low stiffness and modulus of PP. Conventional approaches that incorporate rigid inorganic fillers can enhance the modulus but typically compromise processability and mechanical performance. In this work, we propose a dual strategy by introducing high-modulus organic hydrogenated resin fillers (C9) and applying a biaxial stretching force field. The biaxial stretching process not only promotes PP crystallization but also significantly improves the uniform dispersion of C9 fillers. As a result, a composite paper with ultrafine C9 dispersion and a crystalline self-reinforced structure was successfully fabricated. The composite exhibits a modulus that is 38% higher than that of biaxially stretched neat PP and 218% higher than that of unstretched neat PP. Furthermore, under biaxial stretching, the C9 fillers impart a toughening effect, effectively overcoming the conventional stiffness–toughness trade-off. This work therefore provides a promising strategy for the scalable fabrication of high-performance PP-based synthetic paper.