SEC Filing Details Document Details Form DEF 14A Filing Date Mar 27, 2026 Document Date May 7, 2026 Form Description Official notification to shareholders of matters to be brought to a vote ("Proxy") Filing Group Proxy Filings Company Koppers Holdings, Inc. Issuer Koppers Holdings Inc. Filing Formats iXBRL View HTML Download PDF 6.7 MB Download DOC Download XLS XBRL XBRL Viewer EX-101.SCH - XBRL TAXONOMY EXTENSION SCHEMA EX-101.LAB - XBRL TAXONOMY EXTENSION LABEL LINKBASE DOCUMENT EX-101.PRE - XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE DOCUMENT XML - XBRL INSTANCE DOCUMENT