Question: I have seen Seforim that are inscribed, ‘bought with maaser money’. Is it okay to do that?
Answer: Ideally one should give one’s maaser to the poor (Rema YD 249:1; Minchas Yitzchak 8:83). Today, this includes donations to Torah institutions which will help those who can’t otherwise afford a Torah education.
The Taz (YD 249:1) quotes R’ Menachem of Merseburg that allows one to use one’s maaser to buy Seforim if they cannot otherwise afford to buy them. One doing so must make them available for others to use and write in them that they were bought with maaser funds (See Chafetz Chaim, Ahavas Chesed 2:19:2). R’ Eliezer Waldenberg (Tzitz Eliezer 9:1:2) explains that one who borrows Seforim that they don’t have is considered poor. Such lending is akin to distributing spiritual food, and thus considered a form of Tzedaka.
Most contemporary Poskim hold that as nowadays Seforim are far more accessible, one should not rely on this leniency.
The Aruch Hashulchan (YD 249:10) asks what the difference is between using maaser money for Seforim and other Mitzvos (which is clearly forbidden). Furthermore, what is stopping others from demanding that these Seforim are kept in a Beis Hamedrash so that they are available for all? He thus advises one not to rely on this leniency.R’ Shmuel Wosner (Shevet Halevi 7:194) writes that rather than using one’s maaser money to buy Seforim for oneself, one should buy them and donate them to a Shul or other Torah institution (See Chasam Sofer YD 245).