The screen size does not matter at all. What matters are the font
metrics. Sadly, just because a font has the same name on two machines
does not imply they are the same font. You might ask your PC using
correspondent to send you copies of his Trutype Arial etc. Hide yours
and install his.

Even with identical fonts in your machines, you still may not get the
lines and pages breaking exactly the same on both machines. How can
this be? Two reasons I can think of.
1. One of your printers may be too smart for itself. It may be
substituting its own resident font for yours. I guess this should not
affect line breaks or page breaks, but might make the spacing look
untidy, although compared to Word's native interword performance on
screen it may look simply beautiful.
2. The printers may have different margins - the strip round the
outside of the paper that they can't print on. This may show up in the
printer drivers telling word to make the print area wider or longer for
each page. Usually that results in disappearing footers, but you never
know.

Someone will be along in a minute to say that Word is not meant to keep
the page breaks between machines. Anyone who has ever had to get a Word
CV through a field of vegetables posing as a recruitment agency to a
potential employer with a PA who only knows how to do her nails, knows
that this is simply not meeting ordinary folk's needs.

The 'keep with next' and 'keep lines together' formatting advice is a
useful palliative, but the fact that this question keeps coming up is
evidence that Word is not fit for the purpose that many people want
from it, whether or not it was a design goal of the  product to avoid
rigidly locking the viewers' perceptions of what the author thought was
the finished article.

Like I have said before, I usually ship a PDF[1] as well, so that the
recipient can see how nice it was when it left. Most of them turn my
beautiful Adobe Garamond into Times New Roman, butcher the leading, and
slaughter my carefully crafted heading styles - probably without even
noticing the difference.

Have you ever collaborated on a long document over the phone? "Turn to
page 353.." You mean 349?" Near enough, find a paragraph that starts
"One of your printers may be too smart for itself.. somewhere about
there, you know, just search for it.. oh, you have lost the footnote
reference, in the split pane at the bottom.. oh well.. "

It just is not good enough. It wouldn't be so bad if track changes
worked properly  across platforms and versions and users.

I should get a database of rants. Then I could just say
"insert rant no.4 here"

[1] "Insert rant 7 here".. the one about Word sending eps previews to
PDF instead of the real thing.

where can you get them. the latest version I have of Arial is v2.60
I know my version of Benguiat is old I purchased direct from adobe several years ago.