It is possible that the link they are clicking on is not correctly identifying the file as a PDF file and the browser does not know what to do with it. If the file is a valid pdf file and you tell the browser to open the file with evince it should correctly display the file.
It is possible that the link they are clicking on is not correctly identifying the file as a PDF file and the browser does not know what to do with it. If the file is a valid pdf file and you tell the browser to open the file with evince it should correctly display the file.