A family of Microsoft word processing software products for creating web, email, and print documents.
Since the good news, I have thought of further investigating the difference between the two documents.
Therefore, I've unzipped the docx files involved to look under the hood and there is immediately a glaring difference just by looking at the content of the bundles.
In the case of the original desktop document (document x), this is the content of the word folder within the docx file:
And in the case of the document y, the one resulting simply from opening document x in Word for Android (this is the bad result, not the result where I had set header distance to 0), the folder looks as follows:
I find this to be rather enlightening and not an indicator of simple margin conflicts. Something definitely happens to a document when you open it on Android.