A family of Microsoft word processing software products for creating web, email, and print documents.
Even you say that you cannot identify the words that are missing. So, how do you know that they are missing?
If you are going by word count, that may not be precise.
Are your comparisons between the document as it was in Word 2010 and as it is now in Word 2016, or are they between how you see the document in Word Online and in Word 2016
As far as pages being added, that could well be because the printer that is active in Word 2016 is laying out the document in a different manner to the way that it was laid out in Word 2010
If you want the matter investigated, provide a link to the document in the cloud and send me a copy of the document from Word 2016.