Block pdf download

Is there a way so that the publishers upload a pdf, so it will have its thumbnail generated, but when users click on the page preview it wont allow the pdf to be downloaded, but point up to somewhere else (preferable nothing) maybe the item page itself.

I will develop a foreign plugin to handle the downloads, but I need this as a paleative measure to get the archives online, but blocking the pdfs to be downloaded, but still getting the publishers the possibility to upload their pdfs to feed the archive.

on the live website I see a div download-file where it gets the generated jpg, but links to the .pdf file.

Any tips on the code where those links are generated so i could set up a static link / false link appreciated. I still need the thumb image to be displayed.