Microsoft has lost an appeal against a court judgement that told it to pay $240m (£160m) in damages.
In August 2009, a US court awarded the damages to i4i which claimed Microsoft had infringed its patents.
The patents cover the use of XML, a mark-up language that preserves data formats across different programs.
In this second appeal, the court again re-affirmed the original ruling and spelled out why that decision was made. In court documents spelling out their reasoning, the three appeal court judges said there was evidence that Microsoft knew i4i technology was patented before it turned up in Office programs.