Perhaps you describe issues with accidental selection of pages from the thumbnail images that appear to the left of some Apps - in particular the built-in PDF viewer.
For reasons known only to the Apple Developers, the thumbnail sidebar that you see on the left edge of the screen when using the native PDF viewer cannot be hidden or suppressed. There are no configuration settings to control its behaviour or positioning.
This sidebar was originally to the right of the page - and received frequent complaint from right-handed users; Apple responded by moving the sidebar to the left - now causing issues for the left-handed user community. Many would agree that having choice in positioning either to the left, or right, would largely address difficulties for most users.
Apple do invite constructive comments and feature requests via their Product Feedback portal. For iPad and iPadOS:
Feedback - iPad - Apple