> Second, is it possible to download only pdf files(I
> do not need the gif's and the html's and so on).
> 
> And last, some pdf files are located in the same
> folder but don't have a direct link and are
> downloadable using a search angine in the site. I
> need to download them also. How can I do it?
You can filter out the gifs etc with -*.gif

Unless you have the urls you'll need the htmls

If you can see the directory in your browser then so can httrack.  Most sites
prohibit reading directories.

You can drag the icon from the search results page and use the multiple mirror