The format that Microsoft's Office 2007 programs use to save documents was approved as an international standard Tuesday, a step the company touted as proof it is willing to make once-proprietary technology work openly with competing programs and an important factor for selling to some governments.

But the International Standards Organization (ISO) vote didn't quiet some opponents, who argued that the Office Open XML standard still locks out competitors and gives Microsoft customers no choice but to keep buying its programs forever.

The decision was made public on the Web site of the European standards organization backing the Office Open XML (OOXML) on Tuesday. ISO is expected to formally announce the vote today.

Years before Microsoft started selling Office 2007, its plan to switch to a new way of saving Word, Excel and PowerPoint files sparked concerns that future changes made by the software maker could render government or corporate archives unreadable, especially by non-Microsoft programs.

Making OOXML a standard is meant to ensure that competing programs can read and save OOXML files today and read them far into the future, even if Microsoft moves on.