how do I transfer a PDF document from my laptop to my Ipad?

To copy PDFs to the iPad you first need an app on the iPad that supports PDFs - the iPad doesn't have a file system like a 'normal' computer, everything has to be associated with an app. As to how you then get the PDF to your chosen app will depend upon what the app that you have/get supports - different apps will have different ways of copying their content to/from a computer e.g. via thefile sharingsection at the bottom of the device's apps tab when connected to iTunes, via wifi, email, dropbox etc.

For PDFs there are free apps such as Apple's iBooks app (syncing PDFs to iBooks) and also Adobe Reader - and paid-for apps such as GoodReader.

I email them. PDFs will preview in Mail. To do anything else, you need to follow King_Penguin's instructions.

Get the free "Dropbox" app. Works great!