Add the css code in TNC FlipBook > Global Settings > Custom CSS field to hide the scrollbar. This snippet is for TNC FlipBook - PDF viewer for WordPress: https://codecanyon.net/item/pdf-viewer-for-wordpress/8182815

hide-scrollbar-pvfw.css

/* Hide scrollbar for Chrome, Safari and Opera */
#viewerContainer::-webkit-scrollbar {
  display: none;
}

/* Hide scrollbar for IE, Edge and Firefox */
#viewerContainer {
  -ms-overflow-style: none;  /* IE and Edge */
  scrollbar-width: none;  /* Firefox */
}