Please see Resignation letter of Jogendra Nath Mandal hosted in New Zealand on Wikilivres.
The author of this work, published in 1950, died in 1968, so the work is in the public domain in countries and areas copyrighting for lifetime plus up to 50 years, including New Zealand. However, if published between 1923 and 1977 inclusive, the American non-acceptance of the rule of the shorter term, or the Copyright Term Extension Act if published in the USA with copyright notices and renewals as legally needed, would make this work still considered copyrighted for 95 years after publication, to expire at year end, i.e. to enter the public domain in the USA on January 1, 2046. If created through 1977 but published between 1978 and 2002 inclusive, this work would still considered copyrighted until at least 2047. If published outside the USA, the reason is usually due to the work having not entered the public domain through copyright expiration in its source country or area on January 1, 1996.
For more information, see Cornell University's explanation.