How to track / monitor changes in an on-line PDF file? Need to be notified when that happens.
May be you can retrieve something like the headers and see the modified date? but you will need a script to do that.
You could use the response of a service like http://www.rexswain.com/httpview.html
And read the line:
Probably there is no easy way to do it.
You can consider using LaTex for PDF creation - you will be able to track the "source code" of the PDF as any other source (SVN/Git/ etc.).
You can also use use the pyPdf lib to convert PDF contents to plain text (which is easily track-able).
Sounds like you're trying to use a basic version of source control. This might be a bit too large/complicated for your needs, but have you considered checking in the file to a CVS/SVN repository and then having the users access it through a web interface?