He traveled to Tehran and Bukhara in 1896 and 1897, where he purchased various Hebrew and Judeo-Persian manuscripts and later published descriptive lists of their contents.
These publications provided Western scholars with critical insight into the cultural, literary, and intellectual endeavors pursued by the Jews of Iran.
The manuscripts collected by Adler include both religious and secular works on various topics, including stories, folklore, calendars, biblical and Talmudic dictionaries, prayer books, liturgical hymns, discourses on Kabbalah (Jewish mysticism), and chronicles of religious persecution.
Unfortunately for him, a business associate's embezzlement forced him to sell most of his library to the Jewish Theological Seminary of America in New York City and Hebrew Union College in Cincinnati in 1923.
Adler was extremely active in English-Jewish communal affairs, especially in education, and was an ardent Zionist; he was an early member of the Hovevei Zion in England.