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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ( Mark One ) [ X ] 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 to Commission file number : 001-36199 PULMATRIX , INC . ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of incorporation or organization ) 99 Hayden Avenue , Suite 390 Lexington , MA ( Address of principal executive offices ) 46-1821392 ( I.R.S. Employer Identification No. ) 02421 ( Zip Code ) Registrant's telephone number , including area code ( 781 ) 357-2333 Securities registered pursuant to Section 12 ( b ) of the Exchange Act : Title of each class Common Stock , par value $ 0.0001 per share Name of each exchange on which registered The NASDAQ Stock Market LLC Securities registered pursuant to Section 12 ( g ) of the Exchange 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 [ ] No [ X ] Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Exchange Act . Yes ( ] No [ X ] 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 . Yes [ X ] No [ ] Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted 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 such files ) . Yes [ X ] 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 .