.hidden_pdf_frame{display:none;}
.pdf_preview{
display:block;
overflow:hidden;
position:relative;
}
.pdf_preview:before{
display:block;
content:'';
width:100%;
height:100%;
position:absolute;
top:0;
left:0;    border-right: 25px solid #fff;
}

.pdf_preview embed{
    margin: -1px -1px -1px -1px;
width:100%;height:250px;
}