See http://www.shaunakelly.com/word/shar...matChange.html.

I'll hazard a guess that some (not all) of your users have different
definitions of the same-named styles in their normal.dot templates, *and*
they have the "Automatically Update Document Styles" option turned on. On
those machines, the formatting changes on opening a document. If either of
those conditions doesn't apply, then nothing happens.

--
Regards,
Jay Freedman
Microsoft Word MVP FAQ: http://word.mvps.org

wrote:
We are having a similar problem. When we build and send a Word doc
from one user(different network, different organization, different
legit licences) to another for review or editing, the
formatting/styles changes for no apparent reason on opening the
document. For example: fonts change (yes we have made sure fonts are
installed on both), styles change, blank pages are inserted, etc.
This does not occur with everyone with whom we are exchanging
documents. We can send PDF version of same doc and nothing changes
but the Word version (even a read only file) can behave like this. We
are not novices with Word but must be missing something. TY in
advance for any thoughts.