No extensions allowed

Author: Peter Jabaly (Rutgers Law School)

Autodesk, Inc. v Dassault Systemes SolidWorks Corp. 2009 WL 5218009, 31 December 2009

Citation: Journal of Intellectual Property Law & Practice, doi:10.1093/jiplp/jpq076

A California district court finds that the non-functional use of a file extension (eg marketing and advertising) may be trade marked. Protection, however, may not be extended to the functional uses of file extensions, as when the file extension is necessary to achieve the interoperability of the brand name with the generic version.

Legal context

Where a computer file extension is useful and innately functional, trade mark law, which protects reputation rather than functionality, is inapplicable and any attempt to apply it would inhibit competition.


Software programs store data in files. To locate these files more easily, each file is given a unique name. A file name is generally held in the form of a prefix and suffix separated by a period (eg ‘acrobat.pdf’). The prefix describes the content while the suffix, or file extension, describes the category of data being stored. The purpose of the extension, when combined with the suffix, is to allow the user to identify and locate the file when it is sought. The file names are useful in grouping the files (eg ‘.jpg’ for photos or ‘.dat’ for numerical data). Though programmers follow these conventions for the sake of convenience, they are by no means required to do so and some file extensions are shared among different computer programs. This is unsurprising since there are a limited number of permutations in the three-character file extension.

In this action, Autodesk Inc. sued Dassault Systemes SolidWorks Corp. under a theory of common law trade mark infringement. In its complaint, Autodesk alleged that it held a common law trade mark right in the ‘DWG’ file extension in connection with and related to the marketing and advertising of its AutoCAD program. In its defence, Solidwork maintained out that no one could hold a right to a trade mark that is functional.


At the hearing, Autodesk reluctantly accepted the Court's call to disavow the trade mark law claim and solely pursue a wordmark claim. A wordmark right would provide Autodesk with the exclusive use of the .dwg file extension in connection with its product packaging, marketing, and advertising. In taking this nuanced approach, Autodesk hoped to disarm SolidWork's most compelling argument that registered trade mark law does not apply to functional marks. Autodesk, however, mistakenly believed that it could make this argument without rejecting the claim to full trade mark protection. In other words, Autodesk wanted to have its cake and eat it too, possibly in an effort to obtain a favourable ruling on this narrow legal question, revisiting a larger, more contentious issue later.

The Court did not take kindly to this position in the oral arguments. In the written transcript of the exchange, it strained to understand the legal basis for Autodesk's claim of trade mark infringement. After lengthy semantic wrangling, the plaintiff (through counsel) asserted that other companies may only use the .dwg file extension when it was necessary to the interoperability of the software with Autodesk's own AutoCAD program. Satisfied it had received an admission of an incontrovertible truth, the Court issued an order granting summary judgment in favour of Autodesk 5 days later.

Realizing what it had disclaimed, Autodesk adjusted its argument after-the-fact. After its victory, Autodesk claimed that what it truly meant to assert was that other programmers were only allowed to put ‘.dwg’ at the end of a computer file when ‘the file format is Autodesk's proprietary technology or completely interoperable therewith’. Autodesk blamed its misstatement on the youth and inexperience of the attorney who argued the case. The Court dismissed this scapegoating by restating the doctrine of judicial estoppel, which precludes a party from gaining an advantage by asserting one position and then later—after a tribunal had relied on that position—taking a clearly inconsistent position.

In other words, Autodesk could have made a correction at any time prior to the issuance of the decision. Had that correction been made, the Court would have not ruled in favour of Autodesk because of the functionality issue. No one has the ownership of file extension designations. To do so would contravene the spirit of the Lanham Act and would clog up commerce. Trade mark law seeks to prevent consumer confusion in connection with a commercial transaction. In contrast, file extensions tell the computer the type and the location of a certain file. As the Court succinctly said, ‘A computer is not a consumer’. A computer or a computer user, for that matter, is unconcerned with the maker of the file. The primary function of a file extension is to identify a file.

Practical significance

The case stands for the proposition that file extensions are not eligible for trade mark protection, but may be eligible for wordmark protection. The decision is also a cautionary tale: a winning argument may result in a larger defeat. In order to obtain wordmark protection, Autodesk was required to disavow broader trade mark protection. Further, the case provides a lesson in lawyering. Skirting an issue may be tactful in certain circumstances but, when a favourable outcome hinges on taking a position on a central issue, it is important to consider that issue carefully and take the long view. It is clearly preferable to lose the battle but win the war. Autodesk's counsel took the short view. It made the admission and relinquished Autodesk's colourable claim of right.

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