I've been recently writing a technical document and I wrote something like
It has to be possible to come back to the old version. (paraphrasing here, but I think sense is conveyed)
However MS Word suggested change to
It must be possible to come back to the old version.
I've been looking through the Web, but couldn't find satisfying explanation of this suggestion. I think I understood the difference between I have to... (there is someone external forcing me) vs I must (meaning I have an internal need) but I don't understand how to apply it here.
Could somebody care to explain?