In the wake of Microsoft's vow to support the rival OpenDocument Format in its Office products, European trustbusters said they would examine the move with an eye to determining whether it will loosen the software maker's stranglehold on the desktop applications market.

"The Commission will investigate whether the announced support of Open Document Format in Office leads to better interoperability and allows consumers to process and exchange their documents with the software product of their choice," the European Commission said in a statement.

The announcement came within hours of Microsoft's pledge to add ODF support to its Office 2007 desktop applications suite, which uses a Microsoft version of Extensible Markup Language (XML) as its default file format.

ODF is an open source format backed by Sun Microsystems, IBM, and a number of other vendors. Microsoft's addition of ODF to its Office menu means documents created in Microsoft's Office Open XML format can be opened and edited with ODF-based applications, such as IBM's Lotus Symphony suite.

Microsoft said Wednesday that it would add support for ODF, as well as the XML Paper Specification, Adobe's Portable Document Format, and China's Uniform Office Format, to Office 2007 through a service pack slated for release in the first half of 2009.

"We are committed to providing Office users with greater choice among document formats and enhanced interoperability between those formats and the applications that implement them," said Chris Capossela, a Microsoft senior VP, in a statement.

The company said the decision is "consistent with its interoperability principles."

Microsoft also said it would join groups involved in authoring ODF, including the Organization for the Advancement of Structured Information Standards and the International Organization for Standardization's ODF working group.