Toronto-based i4i scored another victory against Microsoft Tuesday when the U.S. Patent and Trademark Office (PTO) confirmed the validity of an i4i patent that last year briefly put the future of Microsoft Word in jeopardy.

The PTO issued i4i a re-examination certificate, which basically says that the patent it holds is valid. The agency opened an investigation into the issue at the request of Microsoft, which was sued by i4i in 2007 for patent infringement.

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“Put simply Microsoft lost the trial, lost the appeal, and lost the re-examination,” i4i chairman Loudon Owen said in a statement. The decision means that “i4i’s patent is clearly and unequivocally valid.”

Microsoft defended its position.

“We continue to believe there are important matters of patent law that still need to be properly addressed, and we are considering our options for going forward,” Kevin Kutz, director of public affairs for Microsoft, said in a statement.

The case dates back to 2007, when i4i sued Microsoft for infringing on its XML editor patent. In August 2009, a District Court in Texas handed down a $290 million judgment against the software giant and ordered Microsoft to remove Word from the market within 60 days.

Microsoft appealed, but lost in December. At that point, Microsoft said it would remove the infringing XML editor from all copies of Word by January 11, but still filed a second appeal on Jan. 8. In March, the court issued a preliminary ruling that said the original judgment should stand, and in April, it rejected Microsoft’s request for an en banc review.

Microsoft could still appeal to the Supreme Court, a viable but slim possibility.

“The protection of patents and intellectual property is vital to small inventors and pioneers like i4i, especially when confronted by giant infringing industry competitors like Microsoft,” i4i’s Owen concluded.