Query about Word Automation

In my application by word automation using MFC, I need to read from one word document(Source) paragraph by paragraph and then append them to the end of another word document(Target). But I find that I can't append a pragraph to the end of paragraph by InsertParagraphAfter method of Range. The result is that the last paragraph of the target is replaced by the would-append paragraph. Why?

Hi Tang Min,
I do not know how to open Word file using MFC, can you let me know?.
Thanks so much.
Khin Lau