<style type="text/css">.embed-responsive-210by297 { padding-bottom: 141.42%; } </style> <div class="embed-responsive embed-responsive-210by297"> <iframe src="http://PDF檔案網址.pdf"> </iframe> </div>
其他內建比例(不需要<style>那一段):
https://bootstrap.hexschool.com/docs/4.1/utilities/embed/#aspect-ratios