Produces a bitmap owned by the caller for a single TPdfPageDifference from CompareWith
function RenderDiffOverlay(Other: TPdf; const Difference: TPdfPageDifference; const Options: TPdfDocumentDiffOptions): TBitmap;
The selected RenderWidth and RenderHeight determine its size; changed or deleted content is red, inserted content green, and moved pages blue
Visual regions are pixel coordinates from the comparison render; keep its options and input documents unchanged, and release the returned bitmap after displaying or exporting it
The current page selection in each document is restored; invalid indexes or rendering dimensions raise an exception