You can create a new field for that.
create a field bt_pdf and in event onloadrecord set:
{bt_pdf} = “<img src=’…/_lib/img/sys__NM__YOURIMAGE’ onclick='downloadfile(”.{FIELDWITHLINKPDF}.")’ draggable=‘false’ title=‘VIEW FILE:’ />";
and must create a javascript function:
function downloadfile(thefile) {
document.location = thefile;
}