There are a couple of ways to do that.
One is using goodreader to set up a WebDAV server that the thinkpad can connect to. If you open goodreader and hit the "Wifi" icon.. it should start a server that your PC can connect to.
Alternately, you can connect the iPad to your computer and load up iTunes.. click on your iPad, go to the Apps tab.. and scroll down to the File Sharing section.. you should see GoodReader on the list.. click it, then click the "add" button.. and navigate to your PDF.
iTunes should copy the file to your iPad to a place where goodreader can grab it, then when you open goodreader after the transfer is finished, you should see the PDF file in there. (You can do this without forcing a sync.. so you can do it from a different computer than your main one if you're careful. )