property ActualSizeZoom[PageNumber: Integer]: Double;
host screen 上で page を真の physical size で表示する read-only zoom factor です
OS が報告する画面 DPI とページの幅/高さ (ポイント単位) を使って計算されます
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.ActualSizeZoom := {value};
PdfView1.Active := True;
end;