.pdfpreview{
  position: relative;
}
.pdfpreview img {
  display: block;
  margin: 0 auto;
}

.pdfpreview a .fa-download{
  opacity: 0;
  -webkit-transition: opacity 0.5s ease-in-out;
  -moz-transition: opacity 0.5s ease-in-out;
  -o-transition: opacity 0.5s ease-in-out;
  text-align: center;
  font-size: 2.5em;
  padding: 0.5em;
  border-radius: 1em;
  line-height: 1em;
  color: #fff;
  background: #b30410;
  margin: auto;
  position: absolute;
  top: 50%;
  left: 50%;
  z-index: 1;
  -webkit-transform: translate(-50%,-50%);
  -ms-transform: translate(-50%,-50%);
  transform: translate(-50%,-50%);
}

.pdfpreview a:hover .fa-download{
  opacity: 1;
}