property WindowHandle: HWND;
Native window handle of the control (Windows-only).
Available after the control is parented and has been displayed at least once.
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.WindowHandle := {value};
PdfView1.Active := True;
end;