Using DocxMerge I can merge several Docx documents into one Word document. I've modified this to add page breaks between the documents by replacing the end w:body tag with this code:
<w:p><w:r><w:br w:type="page" /></w:r></w:p>
However, the document formatting is not right. For example, one document is centre aligned, and the other is left - they continue with the alignment of whichever document is placed first.
There is also an issue with different margins..
The issue seems to lie with styles.xml however I lack the knowledge of Word XML to merge the two styles.xml. There could be a possibility of saving the word document with styles.xml 'hardcoded' within the main document which would solve the problem.