> We are using the latest release of httrack for
> spidering an existing site structure. We are now
> faced with the necessity of extracting a various
> number of pdf files out of this structure for saving
> it in a different directory.

Check the commandline help for option "-N".  You may want to use either of the
following:

  N4 HTML in web/, images/other in web/xxx, where xxx is the file extension
(all gif will be placed onto web/gif, for example)

  N1004 Identical to N4 exept that there is no "web" directory