It is thought the 'ballot' will form part of a wider move to fend off European Union (EU) antitrust regulators and block massive fines.
In a proposal submitted to the European Commission two weeks ago, Microsoft spelled out a range of promises related to Office, its desktop and server software, and other products to address antitrust concerns first expressed by officials in January 2008.
At that time, the commission announced it had launched a pair of probes into Microsoft's business practices after receiving complaints. One of the investigations revolved around Microsoft's bundling of Internet Explorer (IE) with Windows, and was triggered by a protest filed by Norwegian browser maker Opera.
The other - prompted by a complaint submitted by the European Committee for Interoperable Systems, a trade group that has been vocal about Microsoft's behaviour - involved Office, Microsoft's market-dominant productivity suite.
Microsoft has been accused in the past of favouring its own Office formats to the exclusion of rivals in a way that could hinder the interoperability of its software with other products.
On July 24, Microsoft's general counsel, Brad Smith, announced two deals to the commission, one each on IE and Office.
Microsoft is so confident that its IE proposal will be accepted by the Brussels-based regulators that it has dumped plans to sell a special browser-free version of Windows 7 in the EU this fall. That deal centres on a 'ballot screen', which will let Windows users download and install rival browsers.
Its proposal for Office includes a stipulation similar to the IE ballot; for the suite, it will let European customers select the default file format from an unspecified number of choices. Office 2010 is scheduled to hit the streets next year.
"Beginning with the release of Office , end users that purchase Microsoft's Primary PC Productivity Applications in the EEA [European Economic Area] in both the OEM and retail channel will be prompted in an unbiased way to select default file format (from options that include ODF) for those applications upon the first boot of any one of them," Microsoft said in its proposal.
Microsoft did not spell out how the file format 'ballot' will appear to users, or what choices, other than ODF (Open Document Format), the open-source word processing, spreadsheet and presentation document standard, will be shown.
But the company did promise to provide a tool to corporate IT departments that would let them set the default file format for Office 2010. "Beginning with the Office Customisation Tool released with Office , an updated Office Customisation Tool that will have a mandatory prompt to affirmatively select the default format for file saving for Microsoft's Primary PC Productivity Applications will be made available to IT administrators in EEA," said Microsoft.
Although Microsoft made concessions in May 2008 to support ODF - it made good on them in Office 2007 Service Pack 2 (SP2), which shipped in late April 2009 - EU officials reacted cautiously. "The commission would welcome any step that Microsoft took toward genuine interoperability, more consumer choice and less vendor lock-in," the antitrust agency said last year.
Microsoft's newest offer may hint at an impending resolution to the Office investigation. On the day Microsoft delivered its proposals, the commission said the plan needed "further investigation before the Commission reaches any conclusion as to the next steps", phrasing that the group had not used before when discussing the interoperability inquiry.
Other parts of the proposal outlined additional measures Microsoft will commit to taking, including publishing information on Office's older proprietary file formats as well as the Office Open XML (OOXML) formats that it introduced with Office 2007, and which will be used in Office 2010.
See also: Revealed: what makes Office 2010 great