A computer file extension is inherently functional, therefore a software company that utilizes a particular file extension to designate files that are accessed by its proprietary software may not protect the letters comprising the file extension as a trademark, a district court ruled. The court noted that there are a limited number of letters available to designate file types, and commented: “no one has ownership of file extension designations under the Lanham Act because such designations are inherently functional. Any programmer or computer user anywhere is free to designate file extensions as they see fit, without worrying about trademark violations. File extensions are functional, and functional uses cannot be trademarked.”

Autodesk, Inc. v. Dassault Systemes Solidworks Corp., 2009 U.S. Dist. LEXIS 121541 (N.D. Cal. Dec. 31, 2009) Download PDF