Microsoft will support Adobe's pdf format in the next edition of Office, according to its programme manager Brian Jones.

The move was announced confidentially at the company's MVP conference on Saturday, and made public via Jones' blog later in the day.

"Earlier in this project we decided that while there were already existing third party tools for doing this, we should do the work to build the functionality natively into the product," wrote Jones. "The pdf support will be built into Word, Excel, PowerPoint, Access, Publisher, OneNote, Visio, and InfoPath."

The decision to allow applications such as Word and Excel to save files directly into pdf format - rather than, as now, requiring a separate application to do so - comes as a surprise to industry observers. Microsoft's upcoming XPS technology (formerly codenamed "Metro") has been seen as a direct competitor to Adobe's well-established file formats and publishing technology.

XPS (XML Paper Specification) describes rules for handling files, including viewing, printing, rendering and archiving, and is to be integrated into the upcoming Windows Vista operating system. The system means that the rules for rendering documents for display in Windows will be the same as for rendering for printing purposes, something Microsoft hopes will lend XPS momentum.

Apple has taken a similar path with pdf, making it the basis for the Quartz 2D rendering system in Mac OS X.

Microsoft's Jones said the move showed the company's commitment to open standards, since Office already supports HTML, RTF and new XML-based Microsoft file formats. The theme was echoed by Darren Strange, Microsoft's UK product manager for Office 12. "There has been growing demand from customers for pdf - we are now looking at 120,000 requests per month," Strange said. "It's part of our commitment to open standards, which is a theme running through Office 12."

The decision comes as Microsoft faces the first direct challenge to its lack of direct support for widely used open document standards. The US state of Massachusetts recently said it would only allow the use of office applications supporting either pdf or the newly finalised OpenDocument standard, which directly competes with Microsoft's own XML-based formats.

Since Microsoft has repeatedly said it has no plans to support OpenDocument, Massachusetts' policy would lock out Microsoft Office, the state confirmed in late September. Microsoft's pdf announcement came just over a week after Massachusetts posted the final version of its Enterprise Technical Reference Mode, finalising the open-formats plan. Microsoft's turnaround appears to open the doors once again to Office.

Strange said Microsoft made the pdf decision independently of the Massachusetts policy. "This began quite some time before that high profile customer debate," he said. "It was not really designed to cater for that. The two things are not really related."

Pdf is not a direct competitor with Microsoft's own document formats, because it deals only with static documents. OpenOffice and StarOffice, two related office suites whose development is supported by Sun Microsystems, already support OpenDocument and pdf.

Microsoft also denies that pdf competes with XPS, characterising pdf as a more limited technology that isn't as open as the Microsoft specification. "XPS is an XML standard. It's fully human-readable, it's an open, published schema built on technologies you can take apart programmatically," said Strange. "Pdf is not XML-based. XPS is solving some of the same problems, but it addresses a much bigger picture than pdf is designed for."