.gdpdf-embed {
    position: relative;
    width: 100%;
    padding-top: 129.4%; /* Aspect ratio for U.S. Letter size (8.5:11) */
    overflow: hidden;
}

.gdpdf-embed iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: none;
}