Am I sinful for not extracting documents from someone's phone at work, even though I was able to, which led him to curse me, and is my action considered an injustice to him?

Your refraining from issuing the documents falls into two cases: The first is if it is part of your work obligations. In this case, your refraining is considered negligence and an injustice to the applicant. The second is if the work is a voluntary act of charity and kindness from you. In this case, there is no sin upon you for refraining, and the person's supplication against you is considered an aggression.