Step 1) Do a little research. Google is a good start point
There are a lot of tools already out there
http://www.lmgtfy.com/?q=pdf+to+word[
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as well as a lot of information on the implementation
http://www.lmgtfy.com/?q=how+to+convert+pdf+to+word+document[
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Step 2) Start coding
Step 3) Compile and use the debug to solve little issues
Step 4) When you get a problem you don't know how to solve
but at least you tried it, then come back and ask for something concrete with a snippet of the code giving problems
Sorry if this is not the answer you were looking for. But your question is a bit too wide to be answered at the "Quick" Answers. It is better and you get faster help if you make 10 concrete questions about concrete problems, than a big question about a "how-to guide".
Now that I pay more atention, you did not ask anything.
I recommend you to read following links as well:
What have you tried?[
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How to ask a question?[
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best way to post code snippets[
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They will be very usefull for your future questions