I have this or a similar question too...

My CMS (Ektron) displays document libraries as a list of links.  The links are
formed as: <http://mysite/documents/memos/filename/>. 

Note there is no file extension in the link.  The CMS passes the filename to
an .aspx page when the link is clicked called DownloadAsset.aspx. 
DownloadAsset.aspx evaluated the asset and forms a Response.Addheader that
constructs the Content-Disposition to be inline and the filename plus an
extension. 

So the links in my website don't have file extensions in the page where they
appear.  Almost all the files in these libraries are PDF files.  WinHTTrack
finds all the files, but names them as .html instead of .pdf.

I wonder if there's a way to tell HTTrack to assume the file extension is pdf
when there is no file extension present?