C#.net how to access properties of a file?

Hi..
Problem about c#.net
I want to know how to change the details of a file where we right click the file go to properties window & here we have a summary tab having the details such as title,subject,keywords etc. Now i want to do this through C#.net
Thanks,

I've tried two ways till now, one by opening the responding application.
The other way was using the dsofile.dll from microsoft. With that, first, it
seemed to work. But then I've realized, that if any file properties are read with that dll, the file stays open. Next time i try to read the details i get error saying the file is alrerady open.I've to close my app, and then restart. Than it works again. That's not pretty nice. I set the reader = null in my routine, but it seems so, that this dll keeps the file open somewhere in background.