The only way I know how to do this involves using Dropbox. So, that's the method I'll explain (BTW, if you don't have Dropbox, you can get a 2GB account for free...start by downloading the app from the App Store, then sign up).
1) Have the PDF file in the Public folder of Dropbox
2) Open the Dropbox app on your iPad
3) Navigate to the Public folder and your PDF
4) When the PDF opens in Dropbox's preview pane, press the link icon (upper right) and choose to "Copy Link to Clipboard."
5) Then, open Safari and paste the link in the URL/address bar; press Go
6) When your PDF loads in Safari, select the arrow (to the left of the URL bar) and then select "Add to Home Screen"
7) Name the new icon whatever you wish and press "Add"
Safari will close and you new icon will appear on page 2 of the iPad. You can select it or move it around, just like any other icon.
As long as you never move that PDF out of its spot in Dropbox, that specific link/icon will always go to your PDF file (via Safari).
Hope this helps. Good luck.
Marilyn