No, an outsider cannot use library and reading rooms of IITs, even if it is for educational or other purposes like taking reference or group discussion. Only UG, PG, Doctorates and Faculty of IITs are entitled use of Library. Perhaps, you may not even be able to enter IITs being an outsider nowadays, after COVID, the security arrangements have taken a leap at Most IITs. Institutes like IIT Kharagpur, where even one could elapse Security at Main Gate and Library before and take Way to Library somehow without getting checked, at peak hours, is no more possible now.