A system and method for assembling booklets in document finishers such as saddle staplers includes first and second opposed rollers configured to receive an edge of a stapled crease of a stack of printed documents. The rollers apply both heat and pressure to the crease to form a tight fold. A second set of rollers provides further heat and pressure to the fold to increase tightness even further. Pressure and temperature of one or both roller sets is controllable to accommodate paper stacks having different numbers of pages or different paper characteristics.