We explored the precise impacts of trust and perceived risk on the core constructs of the unified theory of acceptance and use of technology (UTAUT). We applied the UTAUT model to the novel context of the Certified e-Document Authority (CeDA) service used in the Republic of Korea. Our results from structural equation modeling largely supported our hypotheses. Trust and perceived risk were shown to be direct antecedents of intention to use, and trust functioned as an indirect antecedent. Performance expectancy and social influence were shown to positively affect behavioral intention. Effort expectancy was also shown to influence performance expectancy. The combination of trust, perceived risk, performance expectancy, effort expectancy, and social influence accounted for 55.3% of the variance observed in users' intention to use CeDA services.