I had a look and can see the issue you are having. The first thing I noticed is that you have hyphenation turned on. If you turned that off, you would discover that all pages line up as you expect. I suspect you are quite attached to hyphenation so you may not want that as your quick fix.

I hoped that there might be a plausible reason for this - eg. Microsoft doesn't want to split hyphenated words across different pages. It appears this theory doesn't actually bear out so I discarded that theory.

Then I started playing with compatibilitymode to see if that had an effect. I did see pages start to align as expected when I tried different options such as one of the following. In fact, once I started, it didn't appear that I could make page alignment break again.

Activedocument.SetCompatibilityMode wdWord2010
Activedocument.SetCompatibilityMode wdWord2013
Activedocument.SetCompatibilityMode Application.Version

I'm not sure on your version of Word. You have said 2013 but your profile says 2003. All I can say is that you might get some useable results if you try changing compatibility modes on your doc. If you have v2013 then you can try 2007, 2010 and 2013 as all are available to you.

If that fails, perhaps you can do some more googling with hyphenation as a keyword.

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Andrew Lockton
Chrysalis Design, Melbourne Australia