martinibuster - 7:05 am on Sep 20, 2010 (gmt 0)
I think Alex might be talking about a document that is scanned to a PDF file. Web_savvy answered the question. If you have Adobe Acrobat then it should be a simple matter to highlight the text and insert a URL so that it's a live URL. It has to be done manually.
When the document is scanned using a software like PaperPort [nuance.com], the OCR (Optical Character Recognition) part of the software will "read" the image and change it into editable words. PaperPort can also scan a document directly to PDF.
A side note. As I learned it in digital arts class many years ago, PDF files are related to Adobe Illustrator files. They share(d) a common foundation.