3D FlipBook - Issue with Background Scrolling When Viewing PDF on Mobile

When I click on the magazine thumbnail (on the mobile version), the PDF opens normally. However, an annoying scroll issue occurs: while reading the PDF, the background page behind the overlay also moves due to the scroll bar of the page itself.

I would like the full focus to be on the PDF, with zero interference from the background page. How can I completely prevent this unwanted background scrolling?