function FindNext;
Advances the cursor of an in-progress Find session and returns the next matching character index.
Returns -1 when the cursor reaches the end of the document.
Wraps the corresponding PDFium API and exposes it as a TPdf instance member so consumers do not have to manage FPDF_DOCUMENT handles directly.
Pdf1.Active before calling page-scoped operations; methods that require an open document raise EPdfError otherwise.SaveToFile to persist.
if Pdf1.Active then
Pdf1.FindNext;