Q: how to transfer pdf files from ipad to mac

Where are the pdf files on the iPad?

If they are in iBooks, sync with iTunes. If they are in a file sharing app (adobe Reader, Save 2 PDF, GoodReader) - then send them to iTunes within the app and then use the file sharing window in the apps tab of iTunes and you can drag them from the file sharing window in iTunes to your desktop or use the Save to feature.

iOS: About File Sharing

You can also email the files to yourself and use DropBox. The DropBox app is free for the iPad and for the computer as well.

DropBox

If the PDF files were purecahsed from iTunes, you can: from iTunes, select ipad> select apps> scroll down until you find the app containing your pdfs (goodreader, ibooks etc)> select the pdfs you want on your computer> click save to> and it will ask you where on your computer you want to save them

For the noe-purchased PDF files, you have to use third pary app like: iStonsoft iPad to computer transfer, or Amacosft for Mac user:

iStonsoft  iPad to computer transfer:

http://www.istonsoft.com/ipad/transfer-pdf-files-from-ipad-to-pc.html

Amacsoft iPad to Mac transfer:

http://www.amacsoft.com/ipad/transfer-pdf-from-ipad-to-mac.html

and more...