European Union antitrust regulators reacted cautiously Thursday to Microsoft's announcement this week that the software maker will add support for Open Document Format (ODF) to its Office suite next year.

"The Commission would welcome any step that Microsoft took towards genuine interoperability, more consumer choice and less vendor lock-in," the EU's Competition Commission said in a statement.

Wednesday, Microsoft said it would add support for ODF and Adobe Systems' PDF format to Office 2007 in the first half of 2009, the six-month window for launching Office 2007 Service Pack 2 (SP2). The changes will let users open, edit and save those formats -- as well as Microsoft's own XPS (XML Paper Specification) -- without adding translators or other extra code. Users will also be able to set ODF, PDF or XPS as Office's default file format.

The Commission is already investigating claims that Microsoft abused its market-leading position in the application suite business by not providing competitors the technical information they needed to craft software that worked smoothly with Office. That investigation was launched in mid-January after a complaint was filed by the European Committee for Interoperable Systems (ECIS), a trade group whose members include some of Microsoft's longest-running rivals, including Adobe Systems, Corel, IBM, Oracle and Sun Microsystems.

Thursday, EU regulators said that their investigation would continue with an eye on Microsoft's proposed ODF support. "The Commission will investigate whether the announced support of ODF in Office leads to better interoperability and allows consumers to process and exchange their documents with the software product of their choice," the agency's statement continued.

Microsoft did not immediately reply to a call for comment. The ECIS was also not available for comment

However, the ODF Alliance, a group that includes many of the same Microsoft rivals as the ECIS, took a much harsher tone than did the EU.

The ODF Alliance in a statement of its own (download PDF) on Wednesday greeted the news "with skepticism." The group's managing director, Marino Marcich put it plainly: "The proof will be whether and when Microsoft's promised support for ODF is on par with its support for its own format. Governments will be looking for actual results, not promises in press releases.

"Because Microsoft has a history of broken promises, no one should celebrate this news until we see what is actually done and how quickly it is put in place," Marcich added.