Merge PDF files in memory

In my asp.net project I need to merge two PDF file in memory.
1) One is from crystal report which export as A.PDF. This part was finished.
2) Another is from word file. I need to code to read doc file and then convert it to B.PDF in memory.
3) Finally, need to merge A.PDF and B.PDF as one PDF file and then export to file server.
Can someone help me 2) and 3)?