Is the finished .pdf supposed to be real, editable text? Or just a raster scan of the originals (images) ??

If it's just images, then xsane on Linux is totally free, and more than up for the job. It will scan to image files, which are then easily imported into an OpenOffice document, and then saved as .doc, .pdf, or whatever. Zero software cost, and a pretty simple and gentle learning curve.

If text recognition is required (conversion to real, editable text), then xsane can work, but possibly commercial payware *may* do a better job.

Cheers