FORM 10-Q QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 For the quarterly period ended March 31, 2021 Commission file number 1-32737 KOPPERS HOLDINGS INC. (Exact name of registrant as specified in its charter) Pennsylvania 20-1878963 (State of incorporation) (IRS Employer Identification No.) 436 Seventh Avenue Pittsburgh, Pennsylvania 15219 (Address of principal executive offices) (412) 227-2001 ...