Sustainable management of agricultural waste is crucial for environmental protection and economic viability. This work investigates henequen bagasse, a residue from henequen fiber processing, as a source of cellulose to produce reinforced acrylic composite films. Two distinct cellulose extraction methods were assessed: an alkaline hydrothermal treatment (AHTP) and an alkaline extraction procedure (AEP). Comparative analysis of the extracted cellulose was performed, which included evaluations of yield efficiency, crystallinity index, fiber dimensions, and structural morphology. The results demonstrated that AEP provided higher cellulose yields (approximately 43%) with fibers exhibiting a higher aspect ratio (L/D = 73), compared to 37% yield and an aspect ratio of 55 obtained via AHTP. Crystallinity measurements indicated that AHTP cellulose predominantly retained a cellulose I structure with 63% crystallinity, whereas AEP cellulose showed partial transformation to cellulose II, with crystallinity reducing to 44%. Cellulose–acrylic composites were prepared by incorporating the isolated fibers into a commercial acrylic latex. Thermogravimetric analysis (TGA) results showed that adding cellulose did not significantly affect thermal stability. The mechanical performance indicated superior reinforcement for AHTP-derived cellulose at 10 wt%, achieving a maximum elastic modulus of 111 MPa and tensile strength of 6 MPa, albeit with a significant decrease in elongation at break from 435% to 77%. These findings highlight the potential of henequen waste valorization for advanced material development.