property AllowUserPageChange: Boolean;
Allows user input (mouse wheel, scroll bar drag, key bindings) to change the current page.
Set to False when you want to fully drive the page index from code.
All TPdfView display properties trigger a repaint when assigned; you can change several in sequence without flicker because the redraw is coalesced into a single invalidation.
Active := True.PdfView1.Pdf at runtime, re-apply any view-only settings — the new TPdf has its own state.
begin
PdfView1.AllowUserPageChange := {value};
PdfView1.Active := True;
end;