I would add a +1 for testing w/ Word - the official Office suite runs some validation where only Word will show a "broken file" popup, even when nothing else does.
In our case, clients use only real Word, so any machine-generated/mutated files (excel/ppt as well) need a pass through the real office executable.
In our case, clients use only real Word, so any machine-generated/mutated files (excel/ppt as well) need a pass through the real office executable.