[senit] converting PDF files

I'm sorry that this might appear obvious to all you technical wizards out there - we are a VI service and have been relatively fortunate in recieving the PDF files of a number of text books, dierctly from the publishers. The difficulty is that we are having no success in converting these files into a format that allows us to manipulate the material. Any help would be very welcome.
  Many thanks
  Alice Chenneour Randall
  Oxfordshire VISS