UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D. C. 20549 FORM 10-K ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended: December 31, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission file number: 001-3473 HALLADOR ENERGY COMPANY (www.halladorenergy.com) Colorado 84-1014610 (State of incorporation) (IRS Employer Identification No.) 1183 East Canvasback Drive, Terre Haute, I ...