A software company could not assert common-law trademark rights in the software file extension ".dwg" because the file extension was functional, the federal district court in San Francisco has ruled. In a prior summary judgment hearing, the company had disavowed any claims to ownership of a ".dwg" mark when used as a file extension and asserted that it limited its trademark claims to "DWG," as a word mark.

The company was judicially estopped from later maintaining that it had only disavowed uses of ".dwg" when needed to achieve interoperability with the DWG file format defined by the company, the court said. It could not assert that the rest of the world only had a right to put ".dwg" at the end of a computer file when the file format was the company's proprietary technology or completely interoperable with that technology. The company had disclaimed any and all ownership of its putative word mark "DWG" with respect to its use by anyone as a computer file extension, regardless of the format of the file in question.

Even if the company had not made such an unqualified disavowal, file extension designations are inherently functional and not subject to trademark protection, the court said. Even if a file extension served a tangential purpose of communicating the source of the file or file format to consumers, its primary purpose was to identify a file or file type to a computer and its user.

Autodesk, Inc., ND Cal., ¶61,548.