Short answer: You can't.
Longer answer: If you have a commercial version of Acrobat installed you may be able to instantiate a COM object to remotely contol a PDF document and get something out of it. You may also be able to design a COM object that wraps part of the iTextSharp library to parse a PDF file. This is very advanced stuff for someone who has been working with .NET professionally for about 5 years or more.
Tell us more about what you're trying to accomplish.
_________________________________
Yvan Rodrigues · Red Cell Innovation Inc. · L'innovation de Globules Rouges Inc.