The last update to Form N-400, Application for Naturalization, was December 23, 2016. U.S. Citizenship and Immigration Services (USCIS) only accepts the current version of the form. The last major update to the N-400 was on February 4, 2014, when USCIS announced changes that doubled the length of the form. The increase in length stemmed in part from additional questions related to determinations about good moral character and national security. USCIS made additional changes in March 2016 and a new fee schedule went into effect in December 2016.
Also available here are translations of the N-400 by community-based partner organizations. There is also video translation of the 2/4/14 N-400 into Khmer available, courtesy of The Cambodian Family (www.cambodianfamily.org).
A step by step guide to completing the N-400 is available here.