WindowHandle property

Returns the handle inherited from the platform control: VCL supplies a Windows HWND, whilst native LCL supplies its widget set's handle, which must never be passed to Windows APIs

Zero means that the platform widget has not been allocated; parent the viewer and allow its framework to create the widget before using this handle

Use the handle on the UI thread with its matching framework and widget set only; it is separate from PDFium document/page handles and expires when the widget is destroyed

• Widget handles belong to their platform and process; do not store one for reuse in a different process
• Recreating or destroying a widget can alter its handle while the loaded PDF remains unchanged