techidave, I use PDFannotator on my win 8 tablet (with proper stylus) and use it extensively at school.
Typical workflow for me...
set maths test using word
print to pdf using primo (free)
use pdfannotator and stylus to handwrite solutions on the pdf using the tablet/stylus - on my surface pro,writing maths is a very pleasant experience. (this is the connection to your "software to edit pdf" request)
post solutions online
Cuts down heaps on paper, physical storage, keeping track of past tests.
The price - student licence $29 .... 20 licences $458. Don't know if that is cheap or not for you.
tony
EDIT: a url would be nice I s'pose:
http://www.ograhl.com/en/educational.php?Product=pdfannotator