Hi Pradeep
The Word for Developers forum targets programming questions that developers have about how to code Word. Your question belongs in an end-user venue and I will move it to the TechNet forums. You're more likely to find people there who have more experience
with the scenario you describe.
For what it's worth, however: A lot of changes have been made to Word's layout engine in the thirteen or so years between versions. It's quite possible, therefore, that this is affecting how Word generates the automatic line breaks in the document text.
Another possibility is that the document is actively linked to the Normal.dot template and it's picking up formatting information (style defintions) that are different than those that were used in the old version. This would change layout, and perhaps even
font face and size. Should this be the issue, the answer would be to unlink the document from the template in the old version.