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( Mark One ) ý ` 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 , 2020 or TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Large accelerated filer Non - accelerated filer Commission File Number : 001-34146 CLEARWATER PAPER® CLEARWATER PAPER CORPORATION ( Exact name of registrant as specified in its charter ) Delaware 20-3594554 ( State or other jurisdiction of incorporation or organization ) to 601 West Riverside , Suite 1100 Spokane , WA ( Address of principal executive offices ) Trading Symbol CLW ( I.R.S. Employer Identification No. ) ( 509 ) 344-5900 ( Registrant's telephone number , including area code ) Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Common Stock ( $ 0.0001 par value per share ) Securities registered pursuant to Section 12 ( g ) of the Act : None Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . " Yes ý No Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . " Yes ý No Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . ý Yes " No 99201 ( Zip Code ) Name of each exchange on which registered New York Stock Exchange Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S - T ( § 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit and post such files ) . ý Yes " No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Accelerated filer Smaller reporting company Emerging growth company ý If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . ý