The software giant said on Monday that the creation of a fully documented standard submission derived from the formats, called Microsoft Office Open XML, is likely to take about a year.
But Gary Barnett, a research director at analyst firm Ovum, said on Tuesday that he doubted that the move would result in the format becoming "truly open."
"It's a tactical move by Microsoft to give its proprietary document formats a glimmer of openness," Barnett said. He added that Microsoft is entitled to describe its file formats as open only if it "gives up control of its formats to a standards body that is accessible."
If Microsoft maintains control over its XML-based file format, it will be able to arbitrarily change the standard when it wants, enabling it to keep ahead of any competitors that wish to implement the standard, according to Barnett.
Mark Taylor, executive director of the Open Source Consortium , agreed that Microsoft's move is not as open as it might first appear. He said Microsoft appears to want to extend its "Office monopoly into the XML age. If the intention is to really play nicely with others in the open-standards game, then why patent applications in this area?" he asked.
But other industry observers were less critical of Microsoft's move, which follows the growing popularity of the OpenDocument format.
"I think it's great to see that the current discussions have forced Microsoft to be more open," said James Governor, an analyst at RedMonk.
However, Governor pointed out that it was not clear whether any standard approved by ECMA would be compatible with the General Public License, or GPL.
The British Library has also lauded Microsoft's move, saying in a statement that it would help it fulfill its "core responsibility of making our digital collections accessible for generations to come."
So far, Microsoft has refused to support OpenDocument in its software, which Barnett and Taylor believe raises questions about its commitment to open standards.
"The OpenDocument format is a genuinely open format that is managed in a completely transparent way. Any company in this business that is genuine about open standards should be supporting that," Barnett said.
"The existing standard places no restrictions whatsoever on who may implement it, and one has to continue asking the question why Microsoft won't," said Taylor of OpenDocument. "If the Microsoft standard really is genuinely open in the same sense as the OpenDocument format, what advantage is there to Microsoft in trying to impose their standard over the established one?"
Governor suggested that OpenDocument may have an advantage over the Microsoft standard through wider adoption by software makers, but he said this is unlikely to prevent Microsoft Office's Open XML from becoming widespread.
"If we're talking about multiple implementations, OpenDocument has a clear advantage," Governor said. "From a government perspective, the kind of conversations that OpenDocument can have with the public sector will be somewhat more compelling, but Microsoft has shown itself to be very persuasive at selling to the public sector. Also, there are massive advantages in incumbency."
Ingrid Marson of ZDNet UK reported from London.
