s UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 10-K (Mark One) ☒ ANNUAL REPORT UNDER SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended September 30, 2019. ☐ TRANSITION REPORT UNDER SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-38042 ARROWHEAD PHARMACEUTICALS, INC. (Exact name of registrant as specified in its charter) Delaware 46-0408024 (State of incorporation) (I.R.S. ...