Well, you can certainly affect the text flow in Word by specifying
"Keep lines together", "Keep with next", and "Page break before" for
paragraphs. In the user interface, you'll find all of these settings
on the Line and Page Breaks tab of the Paragraph dialog box
(Format>Paragraph). In the Word object model there are KeepTogether,
KeepWithNext, and PageBreakBefore properties defined in the Paragraph,
Paragraphs, and ParagraphFormat classes. Use the VBA Editor and its
help files to learn more.

But you can't prevent Word from inserting page breaks, if that is what
you are trying to do.

The following articles provide some information about how Word lays
out the pages of documents:

Why does the appearance (or layout) of my document change when I open
it on a different machine?
http://word.mvps.org/FAQs/Formatting/TextReflow.htm

Tips and tricks for copy fitting
http://word.mvps.org/FAQs/Formatting/FitCopy.htm