It is possible to activate an iPad without associating it with an account.
iTunes: Turning on Activation-only Mode
But to put PDF files on the iPad you are going to have to load an app to read them. This could be iBooks, which is free, or some other app like GoodReader. To do that you are going to need an account.
You could open the App Store and log in with an account, buy the app, and then log out. Then you could set up an email account, and mail the pdf files, use Open In to get them to the app, and delete the mail account from the iPad when done. The problem with this approach is that the app will always belong to your account, so when an update comes along the person you give the iPad to will not be able to update that app. Eventually they will be forced to delete it, and all the pdf files would go poof, along with any other files they've loaded into it in the interval. It probably wouldn't be annoying enough to counter having got a free iPad, but I doubt they would be amused.
And of course your promotional material is hidden inside the app, where the new owner would either have to stumble across it, or you would need to show them where it is.
The other, easier, no account needed thing you could do is create a link to a promotional web site on the iPad's home page using Safari.
To do this open Safari, navigate to the web site, tap on the box/arrow icon to the left of the URL bar and choose Add to Home Screen. You'll have a chance to name the icon, but there is no way of choosing what the icon will look like.
The links could even be to pdf pages, as long as they are on the web. You may be forced to edit or manually enter the URL to make this happen. I've never tried to do it with a link to a pdf file, so I'm not sure.
It's a pretty good bet that your iPad winner will delete these after a while, or just restore the entire iPad. But your pdf files, or at least the links to them, would be front and center on the Home Screen until then.