Can I copy the PDFs I have on my Mac to the iPad?
There are 3 main routes to get PDF to your iPad:


Drag them into iTunes and have iTunes sync them in the iBooks tab. Other apps will allow management of PDF as files at the bottom of the apps tab in iTunes. 
Use another program like PhoneView to drop them directly to the iPad via USB.
Move them within iOS - mobile mail, mobile safari and other apps will detect that iBooks (and other apps) can read PDF's and offer to move them for you. There are truly hundreds of apps that will receive PDF just like iBooks will. Just a few that are mature, widely adopted and well designed are iDisk, Dropbox, AirSharing but I'll keep this focused on your transport question and leave the comparison of which app on iOS is best for it's own thread. 


Which one is best depends on your workflow, but knowing all three may help you be more nimble.