You need a flat bed scanner (preferably a quite recent model) and the software that applies to it.
Modern applications allow you to scan numberous pages and then output the product as a PDF WITHOUT any specific intervention by you.
I use the HP Photosmart 3310 All-in-One (Fax/Copy/Print/Scan) and PDF is one of th forms of output; when you have finished all the scanning - but you tell it at the start, I think